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Overview
Comment:Continue refactoring where.c in preparation for installing OR-clause optimizations. (CVS 6050)
Downloads: Tarball | ZIP archive | SQL archive
Timelines: family | ancestors | descendants | both | trunk
Files: files | file ages | folders
SHA1: 778e91ddb834f6084ecdf3909692b54bb7da8f6d
User & Date: drh 2008-12-21 03:51:16
References
2019-08-03
14:30 Ticket [71e183ca] MIN() malfunctions for a query with ISNULL condition status still Open with 4 other changes artifact: afd8a0b2 user: drh
Context
2008-12-22
03:37
Fix a variable type to prevent a warning in the proxy-locking code. (CVS 6051) check-in: d9595b96 user: danielk1977 tags: trunk
2008-12-21
03:51
Continue refactoring where.c in preparation for installing OR-clause optimizations. (CVS 6050) check-in: 778e91dd user: drh tags: trunk
2008-12-20
18:33
Add a vfs backend that detects problems like the one addressed by (6043) and (6047). (CVS 6049) check-in: 49172e48 user: danielk1977 tags: trunk
Changes
Hide Diffs Unified Diffs Ignore Whitespace Patch

Changes to src/sqliteInt.h.

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**    May you do good and not evil.
**    May you find forgiveness for yourself and forgive others.
**    May you share freely, never taking more than you give.
**
*************************************************************************
** Internal interface definitions for SQLite.
**
** @(#) $Id: sqliteInt.h,v 1.812 2008/12/20 02:14:40 drh Exp $
*/
#ifndef _SQLITEINT_H_
#define _SQLITEINT_H_

/*
** Include the configuration header output by 'configure' if we're using the
** autoconf-based build
................................................................................
typedef struct TableLock TableLock;
typedef struct Token Token;
typedef struct TriggerStack TriggerStack;
typedef struct TriggerStep TriggerStep;
typedef struct Trigger Trigger;
typedef struct UnpackedRecord UnpackedRecord;
typedef struct Walker Walker;

typedef struct WhereInfo WhereInfo;
typedef struct WhereLevel WhereLevel;

/*
** Defer sourcing vdbe.h and btree.h until after the "u8" and 
** "BusyHandler" typedefs. vdbe.h also requires a few of the opaque
** pointer types (i.e. FuncDef) defined above.
................................................................................
#define JT_CROSS     0x0002    /* Explicit use of the CROSS keyword */
#define JT_NATURAL   0x0004    /* True for a "natural" join */
#define JT_LEFT      0x0008    /* Left outer join */
#define JT_RIGHT     0x0010    /* Right outer join */
#define JT_OUTER     0x0020    /* The "OUTER" keyword is present */
#define JT_ERROR     0x0040    /* unknown or unsupported join type */


























/*
** For each nested loop in a WHERE clause implementation, the WhereInfo
** structure contains a single instance of this structure.  This structure
** is intended to be private the the where.c module and should not be
** access or modified by other modules.
**
** The pIdxInfo and pBestIdx fields are used to help pick the best
** index on a virtual table.  The pIdxInfo pointer contains indexing
** information for the i-th table in the FROM clause before reordering.
** All the pIdxInfo pointers are freed by whereInfoFree() in where.c.
** The pBestIdx pointer is a copy of pIdxInfo for the i-th table after
** FROM clause ordering.  This is a little confusing so I will repeat
** it in different words.  WhereInfo.a[i].pIdxInfo is index information 
** for WhereInfo.pTabList.a[i].  WhereInfo.a[i].pBestInfo is the
** index information for the i-th loop of the join.  pBestInfo is always
** either NULL or a copy of some pIdxInfo.  So for cleanup it is 
** sufficient to free all of the pIdxInfo pointers.
** 
*/
struct WhereLevel {
  u32 wsFlags;          /* "Where-Scan" flags show the choosen scan strategy */

  int iLeftJoin;        /* Memory cell used to implement LEFT OUTER JOIN */
  Index *pIdx;          /* Index used.  NULL if no index */
  struct WhereTerm *pTerm; /* Where term containing OR clause */
  int iTabCur;          /* The VDBE cursor used to access the table */
  int iIdxCur;          /* The VDBE cursor used to access pIdx */
  int addrBrk;          /* Jump here to break out of the loop */
  int addrNxt;          /* Jump here to start the next IN combination */
  int addrCont;         /* Jump here to continue with the next loop cycle */
  int addrFirst;        /* First instruction of interior of the loop */
  int op, p1, p2;       /* Opcode used to terminate the loop */
  u8 p5;                /* P5 operand of the opcode that terminates the loop */
  u8 iFrom;             /* Which entry in the FROM clause */


  u16 nEq;              /* Number of == or IN constraints on this loop */

  u16 nIn;              /* Number of IN operators constraining this loop */
  struct InLoop {
    int iCur;              /* The VDBE cursor used by this IN operator */
    int addrInTop;         /* Top of the IN loop */
  } *aInLoop;           /* Information about each nested IN operator */
  sqlite3_index_info *pBestIdx;  /* Index information for this level */






  /* The following field is really not part of the current level.  But
  ** we need a place to cache index information for each table in the
  ** FROM clause and the WhereLevel structure is a convenient place.


  */
  sqlite3_index_info *pIdxInfo;  /* Index info for n-th source table */
};

/*
** Flags appropriate for the wctrlFlags parameter of sqlite3WhereBegin().
*/
................................................................................
** half does the tail of the WHERE loop.  An instance of
** this structure is returned by the first half and passed
** into the second half to give some continuity.
*/
struct WhereInfo {
  Parse *pParse;       /* Parsing and code generating context */
  u8 okOnePass;        /* Ok to use one-pass algorithm for UPDATE or DELETE */
  SrcList *pTabList;   /* List of tables in the join */
  int iTop;            /* The very beginning of the WHERE loop */
  int iContinue;       /* Jump here to continue with next record */
  int iBreak;          /* Jump here to break out of the loop */
  int nLevel;          /* Number of nested loop */

  sqlite3_index_info **apInfo;  /* Array of pointers to index info structures */
  WhereLevel a[1];     /* Information about each nest loop in the WHERE */
};

/*
** A NameContext defines a context in which to resolve table and column
** names.  The context consists of a list of tables (the pSrcList) field and
** a list of named expression (pEList).  The named expression list may
** be NULL.  The pSrc corresponds to the FROM clause of a SELECT or







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**    May you do good and not evil.
**    May you find forgiveness for yourself and forgive others.
**    May you share freely, never taking more than you give.
**
*************************************************************************
** Internal interface definitions for SQLite.
**
** @(#) $Id: sqliteInt.h,v 1.813 2008/12/21 03:51:16 drh Exp $
*/
#ifndef _SQLITEINT_H_
#define _SQLITEINT_H_

/*
** Include the configuration header output by 'configure' if we're using the
** autoconf-based build
................................................................................
typedef struct TableLock TableLock;
typedef struct Token Token;
typedef struct TriggerStack TriggerStack;
typedef struct TriggerStep TriggerStep;
typedef struct Trigger Trigger;
typedef struct UnpackedRecord UnpackedRecord;
typedef struct Walker Walker;
typedef struct WherePlan WherePlan;
typedef struct WhereInfo WhereInfo;
typedef struct WhereLevel WhereLevel;

/*
** Defer sourcing vdbe.h and btree.h until after the "u8" and 
** "BusyHandler" typedefs. vdbe.h also requires a few of the opaque
** pointer types (i.e. FuncDef) defined above.
................................................................................
#define JT_CROSS     0x0002    /* Explicit use of the CROSS keyword */
#define JT_NATURAL   0x0004    /* True for a "natural" join */
#define JT_LEFT      0x0008    /* Left outer join */
#define JT_RIGHT     0x0010    /* Right outer join */
#define JT_OUTER     0x0020    /* The "OUTER" keyword is present */
#define JT_ERROR     0x0040    /* unknown or unsupported join type */


/*
** A WherePlan object holds information that describes a lookup
** strategy.
**
** This object is intended to be opaque outside of the where.c module.
** It is included here only so that that compiler will know how big it
** is.  None of the fields in this object should be used outside of
** the where.c module.
**
** Within the union, pIdx is only used when wsFlags&WHERE_INDEXED is true.
** pTerm is only used when wsFlags&WHERE_MULTI_OR is true.  And pVtabIdx
** is only used when wsFlags&WHERE_VIRTUALTABLE is true.  It is never the
** case that more than one of these conditions is true.
*/
struct WherePlan {
  u32 wsFlags;                   /* WHERE_* flags that describe the strategy */
  u32 nEq;                       /* Number of == constraints */
  union {
    Index *pIdx;                   /* Index when WHERE_INDEXED is true */
    struct WhereTerm *pTerm;       /* WHERE clause term for OR-search */
    sqlite3_index_info *pVtabIdx;  /* Virtual table index to use */
  } u;
};

/*
** For each nested loop in a WHERE clause implementation, the WhereInfo
** structure contains a single instance of this structure.  This structure
** is intended to be private the the where.c module and should not be
** access or modified by other modules.
**
** The pIdxInfo field is used to help pick the best index on a
** virtual table.  The pIdxInfo pointer contains indexing
** information for the i-th table in the FROM clause before reordering.
** All the pIdxInfo pointers are freed by whereInfoFree() in where.c.
** All other information in the i-th WhereLevel object for the i-th table
** after FROM clause ordering.






*/
struct WhereLevel {

  WherePlan plan;       /* query plan for this element of the FROM clause */
  int iLeftJoin;        /* Memory cell used to implement LEFT OUTER JOIN */


  int iTabCur;          /* The VDBE cursor used to access the table */
  int iIdxCur;          /* The VDBE cursor used to access pIdx */
  int addrBrk;          /* Jump here to break out of the loop */
  int addrNxt;          /* Jump here to start the next IN combination */
  int addrCont;         /* Jump here to continue with the next loop cycle */
  int addrFirst;        /* First instruction of interior of the loop */


  u8 iFrom;             /* Which entry in the FROM clause */
  u8 op, p5;            /* Opcode and P5 of the opcode that ends the loop */
  int p1, p2;           /* Operands of the opcode used to ends the loop */
  union {               /* Information that depends on plan.wsFlags */
    struct {
      int nIn;              /* Number of entries in aInLoop[] */
      struct InLoop {
        int iCur;              /* The VDBE cursor used by this IN operator */
        int addrInTop;         /* Top of the IN loop */
      } *aInLoop;           /* Information about each nested IN operator */

    } in;                 /* Used when plan.wsFlags&WHERE_IN_ABLE */
    struct {
      WherePlan *aPlan;     /* Plans for each term of the WHERE clause */
    } or;                 /* Used when plan.wsFlags&WHERE_MULTI_OR */
  } u;

  /* The following field is really not part of the current level.  But
  ** we need a place to cache virtual table index information for each
  ** virtual table in the FROM clause and the WhereLevel structure is
  ** a convenient place since there is one WhereLevel for each FROM clause
  ** element.
  */
  sqlite3_index_info *pIdxInfo;  /* Index info for n-th source table */
};

/*
** Flags appropriate for the wctrlFlags parameter of sqlite3WhereBegin().
*/
................................................................................
** half does the tail of the WHERE loop.  An instance of
** this structure is returned by the first half and passed
** into the second half to give some continuity.
*/
struct WhereInfo {
  Parse *pParse;       /* Parsing and code generating context */
  u8 okOnePass;        /* Ok to use one-pass algorithm for UPDATE or DELETE */
  SrcList *pTabList;             /* List of tables in the join */
  int iTop;                      /* The very beginning of the WHERE loop */
  int iContinue;                 /* Jump here to continue with next record */
  int iBreak;                    /* Jump here to break out of the loop */
  int nLevel;                    /* Number of nested loop */
  struct WhereClause *pWC;       /* Decomposition of the WHERE clause */
  sqlite3_index_info **apInfo;   /* Array of pointers to index info objects */
  WhereLevel a[1];               /* Information about each nest loop in WHERE */
};

/*
** A NameContext defines a context in which to resolve table and column
** names.  The context consists of a list of tables (the pSrcList) field and
** a list of named expression (pEList).  The named expression list may
** be NULL.  The pSrc corresponds to the FROM clause of a SELECT or

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** This module contains C code that generates VDBE code used to process
** the WHERE clause of SQL statements.  This module is responsible for
** generating the code that loops through a table looking for applicable
** rows.  Indices are selected and used to speed the search when doing
** so is applicable.  Because this module is responsible for selecting
** indices, you might also think of this module as the "query optimizer".
**
** $Id: where.c,v 1.339 2008/12/20 02:06:14 drh Exp $
*/
#include "sqliteInt.h"

/*
** Trace output macros
*/
#if defined(SQLITE_TEST) || defined(SQLITE_DEBUG)
int sqlite3WhereTrace = 0;
#endif
#if 0
# define WHERETRACE(X)  if(sqlite3WhereTrace) sqlite3DebugPrintf X
#else
# define WHERETRACE(X)
#endif

/* Forward reference
*/
typedef struct WhereClause WhereClause;
typedef struct ExprMaskSet ExprMaskSet;
typedef struct WhereOrInfo WhereOrInfo;
typedef struct WhereAndInfo WhereAndInfo;


/*
** The query generator uses an array of instances of this structure to
** help it analyze the subexpressions of the WHERE clause.  Each WHERE
** clause subexpression is separated from the others by AND operators.
** (Note: the same data structure is also reused to hold a group of terms
** separated by OR operators.  But at the top-level, everything is AND
................................................................................
**
** If a term in the WHERE clause does not match either of the two previous
** categories, then eOperator==0.  The WhereTerm.pExpr field is still set
** to the original subexpression content and wtFlags is set up appropriately
** but no other fields in the WhereTerm object are meaningful.
**
** When eOperator!=0, prereqRight and prereqAll record sets of cursor numbers,
** but they do so indirectly.  A single ExprMaskSet structure translates
** cursor number into bits and the translated bit is stored in the prereq
** fields.  The translation is used in order to maximize the number of
** bits that will fit in a Bitmask.  The VDBE cursor numbers might be
** spread out over the non-negative integers.  For example, the cursor
** numbers might be 3, 8, 9, 10, 20, 23, 41, and 45.  The ExprMaskSet
** translates these sparse cursor numbers into consecutive integers
** beginning with 0 in order to make the best possible use of the available
** bits in the Bitmask.  So, in the example above, the cursor numbers
** would be mapped into integers 0 through 7.
**
** The number of terms in a join is limited by the number of bits
** in prereqRight and prereqAll.  The default is 64 bits, hence SQLite
................................................................................

/*
** An instance of the following structure holds all information about a
** WHERE clause.  Mostly this is a container for one or more WhereTerms.
*/
struct WhereClause {
  Parse *pParse;           /* The parser context */
  ExprMaskSet *pMaskSet;   /* Mapping of table indices to bitmasks */
  int nTerm;               /* Number of terms */
  int nSlot;               /* Number of entries in a[] */
  WhereTerm *a;            /* Each a[] describes a term of the WHERE cluase */
  WhereTerm aStatic[4];    /* Initial static space for a[] */
};

/*
** A WhereTerm with eOperator==WO_OR has its u.pOrInfo pointer set to
** a dynamically allocated instance of the following structure.
*/
struct WhereOrInfo {
  WhereClause wc;          /* The OR subexpression broken out */
  Bitmask indexable;       /* Bitmask of all indexable tables in the clause */

};

/*
** A WhereTerm with eOperator==WO_AND has its u.pAndInfo pointer set to
** a dynamically allocated instance of the following structure.
*/
struct WhereAndInfo {
................................................................................
** SrcList_item.iCursor and Expr.iTable fields.  For any given WHERE 
** clause, the cursor numbers might not begin with 0 and they might
** contain gaps in the numbering sequence.  But we want to make maximum
** use of the bits in our bitmasks.  This structure provides a mapping
** from the sparse cursor numbers into consecutive integers beginning
** with 0.
**
** If ExprMaskSet.ix[A]==B it means that The A-th bit of a Bitmask
** corresponds VDBE cursor number B.  The A-th bit of a bitmask is 1<<A.
**
** For example, if the WHERE clause expression used these VDBE
** cursors:  4, 5, 8, 29, 57, 73.  Then the  ExprMaskSet structure
** would map those cursor numbers into bits 0 through 5.
**
** Note that the mapping is not necessarily ordered.  In the example
** above, the mapping might go like this:  4->3, 5->1, 8->2, 29->0,
** 57->5, 73->4.  Or one of 719 other combinations might be used. It
** does not really matter.  What is important is that sparse cursor
** numbers all get mapped into bit numbers that begin with 0 and contain
** no gaps.
*/
struct ExprMaskSet {
  int n;                        /* Number of assigned cursor values */
  int ix[BMS];                  /* Cursor assigned to each bit */
};











/*
** Bitmasks for the operators that indices are able to exploit.  An
** OR-ed combination of these values can be used when searching for
** terms in the where clause.
*/
#define WO_IN     0x001
................................................................................
** join.  Tickets #2177 and #2189.
*/
#define WHERE_ROWID_EQ     0x00001000  /* rowid=EXPR or rowid IN (...) */
#define WHERE_ROWID_RANGE  0x00002000  /* rowid<EXPR and/or rowid>EXPR */
#define WHERE_COLUMN_EQ    0x00010000  /* x=EXPR or x IN (...) */
#define WHERE_COLUMN_RANGE 0x00020000  /* x<EXPR and/or x>EXPR */
#define WHERE_COLUMN_IN    0x00040000  /* x IN (...) */


#define WHERE_TOP_LIMIT    0x00100000  /* x<EXPR or x<=EXPR constraint */
#define WHERE_BTM_LIMIT    0x00200000  /* x>EXPR or x>=EXPR constraint */
#define WHERE_IDX_ONLY     0x00800000  /* Use index only - omit table */
#define WHERE_ORDERBY      0x01000000  /* Output will appear in correct order */
#define WHERE_REVERSE      0x02000000  /* Scan in reverse order */
#define WHERE_UNIQUE       0x04000000  /* Selects no more than one row */
#define WHERE_VIRTUALTABLE 0x08000000  /* Use virtual-table processing */
................................................................................

/*
** Initialize a preallocated WhereClause structure.
*/
static void whereClauseInit(
  WhereClause *pWC,        /* The WhereClause to be initialized */
  Parse *pParse,           /* The parsing context */
  ExprMaskSet *pMaskSet    /* Mapping from table indices to bitmasks */
){
  pWC->pParse = pParse;
  pWC->pMaskSet = pMaskSet;
  pWC->nTerm = 0;
  pWC->nSlot = ArraySize(pWC->aStatic);
  pWC->a = pWC->aStatic;
}
................................................................................

/*
** Deallocate all memory associated with a WhereOrInfo object.
*/
static void whereOrInfoDelete(sqlite3 *db, WhereOrInfo *p){
  if( p ){
    whereClauseClear(&p->wc);

    sqlite3DbFree(db, p);
  }
}

/*
** Deallocate all memory associated with a WhereAndInfo object.
*/
................................................................................
*/
#define initMaskSet(P)  memset(P, 0, sizeof(*P))

/*
** Return the bitmask for the given cursor number.  Return 0 if
** iCursor is not in the set.
*/
static Bitmask getMask(ExprMaskSet *pMaskSet, int iCursor){
  int i;
  for(i=0; i<pMaskSet->n; i++){
    if( pMaskSet->ix[i]==iCursor ){
      return ((Bitmask)1)<<i;
    }
  }
  return 0;
................................................................................
** Create a new mask for cursor iCursor.
**
** There is one cursor per table in the FROM clause.  The number of
** tables in the FROM clause is limited by a test early in the
** sqlite3WhereBegin() routine.  So we know that the pMaskSet->ix[]
** array will never overflow.
*/
static void createMask(ExprMaskSet *pMaskSet, int iCursor){
  assert( pMaskSet->n < ArraySize(pMaskSet->ix) );
  pMaskSet->ix[pMaskSet->n++] = iCursor;
}

/*
** This routine walks (recursively) an expression tree and generates
** a bitmask indicating which tables are used in that expression
................................................................................
** the header comment on that routine for additional information.
** The sqlite3ResolveExprNames() routines looks for column names and
** sets their opcodes to TK_COLUMN and their Expr.iTable fields to
** the VDBE cursor number of the table.  This routine just has to
** translate the cursor numbers into bitmask values and OR all
** the bitmasks together.
*/
static Bitmask exprListTableUsage(ExprMaskSet*, ExprList*);
static Bitmask exprSelectTableUsage(ExprMaskSet*, Select*);
static Bitmask exprTableUsage(ExprMaskSet *pMaskSet, Expr *p){
  Bitmask mask = 0;
  if( p==0 ) return 0;
  if( p->op==TK_COLUMN ){
    mask = getMask(pMaskSet, p->iTable);
    return mask;
  }
  mask = exprTableUsage(pMaskSet, p->pRight);
  mask |= exprTableUsage(pMaskSet, p->pLeft);
  mask |= exprListTableUsage(pMaskSet, p->pList);
  mask |= exprSelectTableUsage(pMaskSet, p->pSelect);
  return mask;
}
static Bitmask exprListTableUsage(ExprMaskSet *pMaskSet, ExprList *pList){
  int i;
  Bitmask mask = 0;
  if( pList ){
    for(i=0; i<pList->nExpr; i++){
      mask |= exprTableUsage(pMaskSet, pList->a[i].pExpr);
    }
  }
  return mask;
}
static Bitmask exprSelectTableUsage(ExprMaskSet *pMaskSet, Select *pS){
  Bitmask mask = 0;
  while( pS ){
    mask |= exprListTableUsage(pMaskSet, pS->pEList);
    mask |= exprListTableUsage(pMaskSet, pS->pGroupBy);
    mask |= exprListTableUsage(pMaskSet, pS->pOrderBy);
    mask |= exprTableUsage(pMaskSet, pS->pWhere);
    mask |= exprTableUsage(pMaskSet, pS->pHaving);
................................................................................
  WhereClause *pWC,         /* the complete WHERE clause */
  int idxTerm               /* Index of the OR-term to be analyzed */
){
  Parse *pParse = pWC->pParse;            /* Parser context */
  sqlite3 *db = pParse->db;               /* Database connection */
  WhereTerm *pTerm = &pWC->a[idxTerm];    /* The term to be analyzed */
  Expr *pExpr = pTerm->pExpr;             /* The expression of the term */
  ExprMaskSet *pMaskSet = pWC->pMaskSet;  /* Table use masks */
  int i;                                  /* Loop counters */
  WhereClause *pOrWc;       /* Breakup of pTerm into subterms */
  WhereTerm *pOrTerm;       /* A Sub-term within the pOrWc */
  WhereOrInfo *pOrInfo;     /* Additional information associated with pTerm */
  Bitmask chngToIN;         /* Tables that might satisfy case 1 */
  Bitmask indexable;        /* Tables that are indexable, satisfying case 2 */

................................................................................
  assert( (pTerm->wtFlags & (TERM_DYNAMIC|TERM_ORINFO|TERM_ANDINFO))==0 );
  assert( pExpr->op==TK_OR );
  pTerm->u.pOrInfo = pOrInfo = sqlite3DbMallocRaw(db, sizeof(*pOrInfo));
  if( pOrInfo==0 ) return;
  pTerm->wtFlags |= TERM_ORINFO;
  pOrWc = &pOrInfo->wc;
  whereClauseInit(pOrWc, pWC->pParse, pMaskSet);

  whereSplit(pOrWc, pExpr, TK_OR);
  exprAnalyzeAll(pSrc, pOrWc);
  if( db->mallocFailed ) return;
  assert( pOrWc->nTerm>=2 );

  /*
  ** Compute the set of tables that might satisfy cases 1 or 2.
................................................................................
        chngToIN &= b;
      }
    }
  }

  /*
  ** Record the set of tables that satisfy case 2.  The set might be
  ** empty, but that is OK.
  */
  pOrInfo->indexable = indexable;
  pTerm->eOperator = WO_OR;

  /*
  ** chngToIN holds a set of tables that *might* satisfy case 1.  But
  ** we have to do some additional checking to see if case 1 really
  ** is satisfied.
  */
  if( chngToIN ){
................................................................................
        pTerm->nChild = 1;
      }else{
        sqlite3ExprListDelete(db, pList);
      }
      pTerm->eOperator = 0;  /* case 1 trumps case 2 */
    }
  }






}
#endif /* !SQLITE_OMIT_OR_OPTIMIZATION && !SQLITE_OMIT_SUBQUERY */


/*
** The input to this routine is an WhereTerm structure with only the
** "pExpr" field filled in.  The job of this routine is to analyze the
................................................................................
*/
static void exprAnalyze(
  SrcList *pSrc,            /* the FROM clause */
  WhereClause *pWC,         /* the WHERE clause */
  int idxTerm               /* Index of the term to be analyzed */
){
  WhereTerm *pTerm;                /* The term to be analyzed */
  ExprMaskSet *pMaskSet;           /* Set of table index masks */
  Expr *pExpr;                     /* The expression to be analyzed */
  Bitmask prereqLeft;              /* Prerequesites of the pExpr->pLeft */
  Bitmask prereqAll;               /* Prerequesites of pExpr */
  Bitmask extraRight = 0;
  int nPattern;
  int isComplete;
  int noCase;
................................................................................

/*
** Return TRUE if any of the expressions in pList->a[iFirst...] contain
** a reference to any table other than the iBase table.
*/
static int referencesOtherTables(
  ExprList *pList,          /* Search expressions in ths list */
  ExprMaskSet *pMaskSet,    /* Mapping from tables to bitmaps */
  int iFirst,               /* Be searching with the iFirst-th expression */
  int iBase                 /* Ignore references to this table */
){
  Bitmask allowed = ~getMask(pMaskSet, iBase);
  while( iFirst<pList->nExpr ){
    if( (exprTableUsage(pMaskSet, pList->a[iFirst++].pExpr)&allowed)!=0 ){
      return 1;
................................................................................
** ASC or DESC.  (Terms of the ORDER BY clause past the end of a UNIQUE
** index do not need to satisfy this constraint.)  The *pbRev value is
** set to 1 if the ORDER BY clause is all DESC and it is set to 0 if
** the ORDER BY clause is all ASC.
*/
static int isSortingIndex(
  Parse *pParse,          /* Parsing context */
  ExprMaskSet *pMaskSet,  /* Mapping from table indices to bitmaps */
  Index *pIdx,            /* The index we are testing */
  int base,               /* Cursor number for the table to be sorted */
  ExprList *pOrderBy,     /* The ORDER BY clause */
  int nEqCol,             /* Number of index columns with == constraints */
  int *pbRev              /* Set to 1 if ORDER BY is DESC */
){
  int i, j;                       /* Loop counters */
................................................................................
** Check table to see if the ORDER BY clause in pOrderBy can be satisfied
** by sorting in order of ROWID.  Return true if so and set *pbRev to be
** true for reverse ROWID and false for forward ROWID order.
*/
static int sortableByRowid(
  int base,               /* Cursor number for table to be sorted */
  ExprList *pOrderBy,     /* The ORDER BY clause */
  ExprMaskSet *pMaskSet,  /* Mapping from tables to bitmaps */
  int *pbRev              /* Set to 1 if ORDER BY is DESC */
){
  Expr *p;

  assert( pOrderBy!=0 );
  assert( pOrderBy->nExpr>0 );
  p = pOrderBy->a[0].pExpr;
................................................................................

  *(int*)&pIdxInfo->nOrderBy = nOrderBy;
  return pIdxInfo->estimatedCost;
}
#endif /* SQLITE_OMIT_VIRTUALTABLE */

/*
** Find the best index for accessing a particular table.  Return a pointer
** to the index, flags that describe how the index should be used, the
** number of equality constraints, and the "cost" for this index.
**
** The lowest cost index wins.  The cost is an estimate of the amount of
** CPU and disk I/O need to process the request using the selected index.
** Factors that influence cost include:
**
**    *  The estimated number of rows that will be retrieved.  (The
**       fewer the better.)
**
**    *  Whether or not sorting must occur.
**
**    *  Whether or not there must be separate lookups in the
**       index and in the main table.
**
** If there was an INDEXED BY clause attached to the table in the SELECT
** statement, then this function only considers strategies using the 
** named index. If one cannot be found, then the returned cost is
** SQLITE_BIG_DBL. If a strategy can be found that uses the named index, 
** then the cost is calculated in the usual way.
**
** If a NOT INDEXED clause was attached to the table in the SELECT 
** statement, then no indexes are considered. However, the selected 
** stategy may still take advantage of the tables built-in rowid
** index.
*/
static double bestIndex(
  Parse *pParse,              /* The parsing context */
  WhereClause *pWC,           /* The WHERE clause */
  struct SrcList_item *pSrc,  /* The FROM clause term to search */
  Bitmask notReady,           /* Mask of cursors that are not available */
  ExprList *pOrderBy,         /* The order by clause */
  Index **ppIndex,            /* Make *ppIndex point to the best index */
  int *pWsFlags,              /* Put wsFlags describing scan strategy here */
  int *pnEq                   /* Put the number of == or IN constraints here */
){
  WhereTerm *pTerm;
  Index *bestIdx = 0;         /* Index that gives the lowest cost */
  double lowestCost;          /* The cost of using bestIdx */
  int bestWsFlags = 0;        /* Flags associated with bestIdx */
  int bestNEq = 0;            /* Best value for nEq */
  int iCur = pSrc->iCursor;   /* The cursor of the table to be accessed */
  Index *pProbe;              /* An index we are evaluating */
  int rev;                    /* True to scan in reverse order */
  int wsFlags;                /* Flags associated with pProbe */
  int nEq;                    /* Number of == or IN constraints */
  int eqTermMask;             /* Mask of valid equality operators */
  double cost;                /* Cost of using pProbe */


  WHERETRACE(("bestIndex: tbl=%s notReady=%llx\n", pSrc->pTab->zName,notReady));
  lowestCost = SQLITE_BIG_DBL;
  pProbe = pSrc->pTab->pIndex;
  if( pSrc->notIndexed ){
    pProbe = 0;
  }

  /* If the table has no indices and there are no terms in the where
  ** clause that refer to the ROWID, then we will never be able to do
  ** anything other than a full table scan on this table.  We might as
  ** well put it first in the join order.  That way, perhaps it can be
  ** referenced by other tables in the join.
  */

  if( pProbe==0 &&
     findTerm(pWC, iCur, -1, 0, WO_EQ|WO_IN|WO_LT|WO_LE|WO_GT|WO_GE,0)==0 &&
     (pOrderBy==0 || !sortableByRowid(iCur, pOrderBy, pWC->pMaskSet, &rev)) ){
    *pWsFlags = 0;
    *ppIndex = 0;
    *pnEq = 0;
    return 0.0;
  }


  /* Check for a rowid=EXPR or rowid IN (...) constraints. If there was
  ** an INDEXED BY clause attached to this table, skip this step.
  */
  if( !pSrc->pIndex ){
    pTerm = findTerm(pWC, iCur, -1, notReady, WO_EQ|WO_IN, 0);
    if( pTerm ){
      Expr *pExpr;
      *ppIndex = 0;
      bestWsFlags = WHERE_ROWID_EQ;
      if( pTerm->eOperator & WO_EQ ){
        /* Rowid== is always the best pick.  Look no further.  Because only
        ** a single row is generated, output is always in sorted order */
        *pWsFlags = WHERE_ROWID_EQ | WHERE_UNIQUE;
        *pnEq = 1;
        WHERETRACE(("... best is rowid\n"));


        return 0.0;
      }else if( (pExpr = pTerm->pExpr)->pList!=0 ){
        /* Rowid IN (LIST): cost is NlogN where N is the number of list
        ** elements.  */
        lowestCost = pExpr->pList->nExpr;
        lowestCost *= estLog(lowestCost);
      }else{
        /* Rowid IN (SELECT): cost is NlogN where N is the number of rows
        ** in the result of the inner select.  We have no way to estimate
        ** that value so make a wild guess. */

        lowestCost = 200;
      }
      WHERETRACE(("... rowid IN cost: %.9g\n", lowestCost));
    }
  
    /* Estimate the cost of a table scan.  If we do not know how many
    ** entries are in the table, use 1 million as a guess.
    */
    cost = pProbe ? pProbe->aiRowEst[0] : 1000000;
    WHERETRACE(("... table scan base cost: %.9g\n", cost));
................................................................................
        wsFlags |= WHERE_BTM_LIMIT;
        cost /= 3;  /* Guess that rowid>EXPR eliminates two-thirds of rows */
      }
      WHERETRACE(("... rowid range reduces cost to %.9g\n", cost));
    }else{
      wsFlags = 0;
    }

  
    /* If the table scan does not satisfy the ORDER BY clause, increase
    ** the cost by NlogN to cover the expense of sorting. */
    if( pOrderBy ){
      if( sortableByRowid(iCur, pOrderBy, pWC->pMaskSet, &rev) ){
        wsFlags |= WHERE_ORDERBY|WHERE_ROWID_RANGE;
        if( rev ){
................................................................................
          wsFlags |= WHERE_REVERSE;
        }
      }else{
        cost += cost*estLog(cost);
        WHERETRACE(("... sorting increases cost to %.9g\n", cost));
      }
    }
    if( cost<lowestCost ){
      lowestCost = cost;

      bestWsFlags = wsFlags;
    }
  }

  /* If the pSrc table is the right table of a LEFT JOIN then we may not
  ** use an index to satisfy IS NULL constraints on that table.  This is
  ** because columns might end up being NULL if the table does not match -
  ** a circumstance which the index cannot help us discover.  Ticket #2177.
................................................................................
        if( pExpr->pSelect!=0 ){
          inMultiplier *= 25;
        }else if( ALWAYS(pExpr->pList) ){
          inMultiplier *= pExpr->pList->nExpr + 1;
        }
      }
    }
    cost = pProbe->aiRowEst[i] * inMultiplier * estLog(inMultiplier);

    nEq = i;
    if( pProbe->onError!=OE_None && (wsFlags & WHERE_COLUMN_IN)==0
         && nEq==pProbe->nColumn ){
      wsFlags |= WHERE_UNIQUE;
    }
    WHERETRACE(("...... nEq=%d inMult=%.9g cost=%.9g\n",nEq,inMultiplier,cost));

................................................................................
      int j = pProbe->aiColumn[nEq];
      pTerm = findTerm(pWC, iCur, j, notReady, WO_LT|WO_LE|WO_GT|WO_GE, pProbe);
      if( pTerm ){
        wsFlags |= WHERE_COLUMN_RANGE;
        if( findTerm(pWC, iCur, j, notReady, WO_LT|WO_LE, pProbe) ){
          wsFlags |= WHERE_TOP_LIMIT;
          cost /= 3;

        }
        if( findTerm(pWC, iCur, j, notReady, WO_GT|WO_GE, pProbe) ){
          wsFlags |= WHERE_BTM_LIMIT;
          cost /= 3;

        }
        WHERETRACE(("...... range reduces cost to %.9g\n", cost));
      }
    }

    /* Add the additional cost of sorting if that is a factor.
    */
................................................................................
        cost /= 2;
        WHERETRACE(("...... idx-only reduces cost to %.9g\n", cost));
      }
    }

    /* If this index has achieved the lowest cost so far, then use it.
    */
    if( wsFlags && cost < lowestCost ){
      bestIdx = pProbe;
      lowestCost = cost;

      bestWsFlags = wsFlags;
      bestNEq = nEq;


    }
  }

  /* Report the best result
  */
  *ppIndex = bestIdx;
  WHERETRACE(("best index is %s, cost=%.9g, wsFlags=%x, nEq=%d\n",

        bestIdx ? bestIdx->zName : "(none)", lowestCost, bestWsFlags, bestNEq));
  *pWsFlags = bestWsFlags | eqTermMask;
  *pnEq = bestNEq;
  return lowestCost;
}


/*
** Disable a term in the WHERE clause.  Except, do not disable the term
** if it controls a LEFT OUTER JOIN and it did not originate in the ON
** or USING clause of that join.
................................................................................

    assert( pX->op==TK_IN );
    iReg = iTarget;
    eType = sqlite3FindInIndex(pParse, pX, 0);
    iTab = pX->iTable;
    sqlite3VdbeAddOp2(v, OP_Rewind, iTab, 0);
    VdbeComment((v, "%.*s", pX->span.n, pX->span.z));

    if( pLevel->nIn==0 ){
      pLevel->addrNxt = sqlite3VdbeMakeLabel(v);
    }
    pLevel->nIn++;

    pLevel->aInLoop = sqlite3DbReallocOrFree(pParse->db, pLevel->aInLoop,
                                    sizeof(pLevel->aInLoop[0])*pLevel->nIn);
    pIn = pLevel->aInLoop;
    if( pIn ){
      pIn += pLevel->nIn - 1;
      pIn->iCur = iTab;
      if( eType==IN_INDEX_ROWID ){
        pIn->addrInTop = sqlite3VdbeAddOp2(v, OP_Rowid, iTab, iReg);
      }else{
        pIn->addrInTop = sqlite3VdbeAddOp3(v, OP_Column, iTab, 0, iReg);
      }
      sqlite3VdbeAddOp1(v, OP_IsNull, iReg);
    }else{
      pLevel->nIn = 0;
    }
#endif
  }
  disableTerm(pLevel, pTerm);
  return iReg;
}

................................................................................
static int codeAllEqualityTerms(
  Parse *pParse,        /* Parsing context */
  WhereLevel *pLevel,   /* Which nested loop of the FROM we are coding */
  WhereClause *pWC,     /* The WHERE clause */
  Bitmask notReady,     /* Which parts of FROM have not yet been coded */
  int nExtraReg         /* Number of extra registers to allocate */
){
  int nEq = pLevel->nEq;        /* The number of == or IN constraints to code */
  Vdbe *v = pParse->pVdbe;      /* The virtual machine under construction */
  Index *pIdx = pLevel->pIdx;   /* The index being used for this loop */
  int iCur = pLevel->iTabCur;   /* The cursor of the table */
  WhereTerm *pTerm;             /* A single constraint term */
  int j;                        /* Loop counter */
  int regBase;                  /* Base register */





  /* Figure out how many memory cells we will need then allocate them.
  ** We always need at least one used to store the loop terminator
  ** value.  If there are IN operators we'll need one for each == or
  ** IN constraint.
  */
  regBase = pParse->nMem + 1;
  pParse->nMem += pLevel->nEq + 1 + nExtraReg;

  /* Evaluate the equality constraints
  */
  assert( pIdx->nColumn>=nEq );
  for(j=0; j<nEq; j++){
    int r1;
    int k = pIdx->aiColumn[j];
    pTerm = findTerm(pWC, iCur, k, notReady, pLevel->wsFlags, pIdx);
    if( NEVER(pTerm==0) ) break;
    assert( (pTerm->wtFlags & TERM_CODED)==0 );
    r1 = codeEqualityTerm(pParse, pTerm, pLevel, regBase+j);
    if( r1!=regBase+j ){
      sqlite3VdbeAddOp2(v, OP_SCopy, r1, regBase+j);
    }
    testcase( pTerm->eOperator & WO_ISNULL );
................................................................................
    testcase( pTerm->eOperator & WO_IN );
    if( (pTerm->eOperator & (WO_ISNULL|WO_IN))==0 ){
      sqlite3VdbeAddOp2(v, OP_IsNull, regBase+j, pLevel->addrBrk);
    }
  }
  return regBase;
}


















































































































































































































































































































































































































































































































#if defined(SQLITE_TEST)
/*
** The following variable holds a text description of query plan generated
** by the most recent call to sqlite3WhereBegin().  Each call to WhereBegin
** overwrites the previous.  This information is used for testing and
** analysis only.
................................................................................
    for(i=0; i<pWInfo->nLevel; i++){
      sqlite3_index_info *pInfo = pWInfo->a[i].pIdxInfo;
      if( pInfo ){
        assert( pInfo->needToFreeIdxStr==0 );
        sqlite3DbFree(db, pInfo);
      }
    }

    sqlite3DbFree(db, pWInfo);
  }
}


/*
** Generate the beginning of the loop used for WHERE clause processing.
................................................................................
  Expr *pWhere,         /* The WHERE clause */
  ExprList **ppOrderBy, /* An ORDER BY clause, or NULL */
  u8 wctrlFlags         /* One of the WHERE_* flags defined in sqliteInt.h */
){
  int i;                     /* Loop counter */
  WhereInfo *pWInfo;         /* Will become the return value of this function */
  Vdbe *v = pParse->pVdbe;   /* The virtual database engine */
  int addrBrk, addrCont = 0; /* Addresses used during code generation */
  Bitmask notReady;          /* Cursors that are not yet positioned */
  WhereTerm *pTerm;          /* A single term in the WHERE clause */
  ExprMaskSet maskSet;       /* The expression mask set */
  WhereClause wc;            /* The WHERE clause is divided into these terms */

  struct SrcList_item *pTabItem;  /* A single entry from pTabList */
  WhereLevel *pLevel;             /* A single level in the pWInfo list */
  int iFrom;                      /* First unused FROM clause element */
  int andFlags;              /* AND-ed combination of all wc.a[].wtFlags */
  sqlite3 *db;               /* Database connection */
  ExprList *pOrderBy = 0;

  /* The number of tables in the FROM clause is limited by the number of
  ** bits in a Bitmask 
  */
  if( pTabList->nSrc>BMS ){
................................................................................
    return 0;
  }

  if( ppOrderBy ){
    pOrderBy = *ppOrderBy;
  }

  /* Split the WHERE clause into separate subexpressions where each
  ** subexpression is separated by an AND operator.
  */
  initMaskSet(&maskSet);
  whereClauseInit(&wc, pParse, &maskSet);
  sqlite3ExprCodeConstants(pParse, pWhere);
  whereSplit(&wc, pWhere, TK_AND);
    
  /* Allocate and initialize the WhereInfo structure that will become the
  ** return value.
  */
  db = pParse->db;
  pWInfo = sqlite3DbMallocZero(db,  
                      sizeof(WhereInfo) + pTabList->nSrc*sizeof(WhereLevel));




  if( db->mallocFailed ){
    goto whereBeginError;
  }
  pWInfo->nLevel = pTabList->nSrc;
  pWInfo->pParse = pParse;
  pWInfo->pTabList = pTabList;
  pWInfo->iBreak = sqlite3VdbeMakeLabel(v);











  /* Special case: a WHERE clause that is constant.  Evaluate the
  ** expression and either jump over all of the code or fall thru.
  */
  if( pWhere && (pTabList->nSrc==0 || sqlite3ExprIsConstantNotJoin(pWhere)) ){
    sqlite3ExprIfFalse(pParse, pWhere, pWInfo->iBreak, SQLITE_JUMPIFNULL);
    pWhere = 0;
  }
................................................................................
  ** is (X-1).   An expression from the ON clause of a LEFT JOIN can use
  ** its Expr.iRightJoinTable value to find the bitmask of the right table
  ** of the join.  Subtracting one from the right table bitmask gives a
  ** bitmask for all tables to the left of the join.  Knowing the bitmask
  ** for all tables to the left of a left join is important.  Ticket #3015.
  */
  for(i=0; i<pTabList->nSrc; i++){
    createMask(&maskSet, pTabList->a[i].iCursor);
  }
#ifndef NDEBUG
  {
    Bitmask toTheLeft = 0;
    for(i=0; i<pTabList->nSrc; i++){
      Bitmask m = getMask(&maskSet, pTabList->a[i].iCursor);
      assert( (m-1)==toTheLeft );
      toTheLeft |= m;
    }
  }
#endif

  /* Analyze all of the subexpressions.  Note that exprAnalyze() might
  ** add new virtual terms onto the end of the WHERE clause.  We do not
  ** want to analyze these virtual terms, so start analyzing at the end
  ** and work forward so that the added virtual terms are never processed.
  */
  exprAnalyzeAll(pTabList, &wc);
  if( db->mallocFailed ){
    goto whereBeginError;
  }

  /* Chose the best index to use for each table in the FROM clause.
  **
  ** This loop fills in the following fields:
................................................................................
  **
  **   pWInfo->a[].pIdx      The index to use for this level of the loop.
  **   pWInfo->a[].wsFlags   WHERE_xxx flags associated with pIdx
  **   pWInfo->a[].nEq       The number of == and IN constraints
  **   pWInfo->a[].iFrom     Which term of the FROM clause is being coded
  **   pWInfo->a[].iTabCur   The VDBE cursor for the database table
  **   pWInfo->a[].iIdxCur   The VDBE cursor for the index

  **
  ** This loop also figures out the nesting order of tables in the FROM
  ** clause.
  */
  notReady = ~(Bitmask)0;
  pTabItem = pTabList->a;
  pLevel = pWInfo->a;
  andFlags = ~0;
  WHERETRACE(("*** Optimizer Start ***\n"));
  for(i=iFrom=0, pLevel=pWInfo->a; i<pTabList->nSrc; i++, pLevel++){

    Index *pIdx;                /* Index for FROM table at pTabItem */
    int wsFlags;                /* Flags describing scan strategy */
    int nEq;                    /* Number of == or IN constraints */
    double cost;                /* The cost for pIdx */
    int j;                      /* For looping over FROM tables */
    Index *pBest = 0;           /* The best index seen so far */
    int bestWsFlags = 0;        /* Flags associated with pBest */
    int bestNEq = 0;            /* nEq associated with pBest */
    double lowestCost;          /* Cost of the pBest */
    int bestJ = 0;              /* The value of j */
    Bitmask m;                  /* Bitmask value for j or bestJ */
    int once = 0;               /* True when first table is seen */
    sqlite3_index_info *pIndex; /* Current virtual index */


    lowestCost = SQLITE_BIG_DBL;
    for(j=iFrom, pTabItem=&pTabList->a[j]; j<pTabList->nSrc; j++, pTabItem++){
      int doNotReorder;  /* True if this table should not be reordered */


      doNotReorder =  (pTabItem->jointype & (JT_LEFT|JT_CROSS))!=0;
      if( once && doNotReorder ) break;
      m = getMask(&maskSet, pTabItem->iCursor);
      if( (m & notReady)==0 ){
        if( j==iFrom ) iFrom++;
        continue;
      }
      assert( pTabItem->pTab );
#ifndef SQLITE_OMIT_VIRTUALTABLE
      if( IsVirtual(pTabItem->pTab) ){

        sqlite3_index_info **ppIdxInfo = &pWInfo->a[j].pIdxInfo;
        cost = bestVirtualIndex(pParse, &wc, pTabItem, notReady,
                                ppOrderBy ? *ppOrderBy : 0, i==0,
                                ppIdxInfo);
        wsFlags = WHERE_VIRTUALTABLE;
        pIndex = *ppIdxInfo;
        if( pIndex && pIndex->orderByConsumed ){
          wsFlags = WHERE_VIRTUALTABLE | WHERE_ORDERBY;
        }
        pIdx = 0;
        nEq = 0;
        if( (SQLITE_BIG_DBL/2.0)<cost ){
          /* The cost is not allowed to be larger than SQLITE_BIG_DBL (the
          ** inital value of lowestCost in this loop. If it is, then
          ** the (cost<lowestCost) test below will never be true and
          ** pLevel->pBestIdx never set.
          */ 
          cost = (SQLITE_BIG_DBL/2.0);
        }
      }else 
#endif
      {
        cost = bestIndex(pParse, &wc, pTabItem, notReady,
                         (i==0 && ppOrderBy) ? *ppOrderBy : 0,
                         &pIdx, &wsFlags, &nEq);
        pIndex = 0;
      }
      if( cost<lowestCost ){

        once = 1;
        lowestCost = cost;
        pBest = pIdx;
        bestWsFlags = wsFlags;
        bestNEq = nEq;

        bestJ = j;
        pLevel->pBestIdx = pIndex;
      }
      if( doNotReorder ) break;
    }
    WHERETRACE(("*** Optimizer selects table %d for loop %d\n", bestJ,
           pLevel-pWInfo->a));
    if( (bestWsFlags & WHERE_ORDERBY)!=0 ){
      *ppOrderBy = 0;
    }
    andFlags &= bestWsFlags;
    pLevel->wsFlags = bestWsFlags;
    pLevel->pIdx = pBest;
    pLevel->nEq = bestNEq;
    pLevel->aInLoop = 0;
    pLevel->nIn = 0;
    if( pBest ){
      pLevel->iIdxCur = pParse->nTab++;
    }else{
      pLevel->iIdxCur = -1;
    }
    notReady &= ~getMask(&maskSet, pTabList->a[bestJ].iCursor);
    pLevel->iFrom = bestJ;

    /* Check that if the table scanned by this loop iteration had an
    ** INDEXED BY clause attached to it, that the named index is being
    ** used for the scan. If not, then query compilation has failed.
    ** Return an error.
    */
    pIdx = pTabList->a[bestJ].pIndex;
    assert( !pIdx || !pBest || pIdx==pBest );


    if( pIdx && pBest!=pIdx ){



      sqlite3ErrorMsg(pParse, "cannot use index: %s", pIdx->zName);
      goto whereBeginError;
    }
  }
  WHERETRACE(("*** Optimizer Finished ***\n"));

  /* If the total query only selects a single row, then the ORDER BY
................................................................................
  ** to use a one-pass algorithm, determine if this is appropriate.
  ** The one-pass algorithm only works if the WHERE clause constraints
  ** the statement to update a single row.
  */
  assert( (wctrlFlags & WHERE_ONEPASS_DESIRED)==0 || pWInfo->nLevel==1 );
  if( (wctrlFlags & WHERE_ONEPASS_DESIRED)!=0 && (andFlags & WHERE_UNIQUE)!=0 ){
    pWInfo->okOnePass = 1;
    pWInfo->a[0].wsFlags &= ~WHERE_IDX_ONLY;
  }

  /* Open all tables in the pTabList and any indices selected for
  ** searching those tables.
  */
  sqlite3CodeVerifySchema(pParse, -1); /* Insert the cookie verifier Goto */
  for(i=0, pLevel=pWInfo->a; i<pTabList->nSrc; i++, pLevel++){
    Table *pTab;     /* Table to open */
    Index *pIx;      /* Index used to access pTab (if any) */
    int iDb;         /* Index of database containing table/index */
    int iIdxCur = pLevel->iIdxCur;

#ifndef SQLITE_OMIT_EXPLAIN
    if( pParse->explain==2 ){
      char *zMsg;
      struct SrcList_item *pItem = &pTabList->a[pLevel->iFrom];
      zMsg = sqlite3MPrintf(db, "TABLE %s", pItem->zName);
      if( pItem->zAlias ){
        zMsg = sqlite3MAppendf(db, zMsg, "%s AS %s", zMsg, pItem->zAlias);
      }
      if( (pIx = pLevel->pIdx)!=0 ){
        zMsg = sqlite3MAppendf(db, zMsg, "%s WITH INDEX %s", zMsg, pIx->zName);

      }else if( pLevel->wsFlags & (WHERE_ROWID_EQ|WHERE_ROWID_RANGE) ){
        zMsg = sqlite3MAppendf(db, zMsg, "%s USING PRIMARY KEY", zMsg);
      }
#ifndef SQLITE_OMIT_VIRTUALTABLE
      else if( pLevel->pBestIdx ){
        sqlite3_index_info *pBestIdx = pLevel->pBestIdx;
        zMsg = sqlite3MAppendf(db, zMsg, "%s VIRTUAL TABLE INDEX %d:%s", zMsg,
                    pBestIdx->idxNum, pBestIdx->idxStr);
      }
#endif
      if( pLevel->wsFlags & WHERE_ORDERBY ){
        zMsg = sqlite3MAppendf(db, zMsg, "%s ORDER BY", zMsg);
      }
      sqlite3VdbeAddOp4(v, OP_Explain, i, pLevel->iFrom, 0, zMsg, P4_DYNAMIC);
    }
#endif /* SQLITE_OMIT_EXPLAIN */
    pTabItem = &pTabList->a[pLevel->iFrom];
    pTab = pTabItem->pTab;
    iDb = sqlite3SchemaToIndex(pParse->db, pTab->pSchema);
    if( (pTab->tabFlags & TF_Ephemeral)!=0 || pTab->pSelect ) continue;
#ifndef SQLITE_OMIT_VIRTUALTABLE
    if( pLevel->pBestIdx ){
      int iCur = pTabItem->iCursor;
      sqlite3VdbeAddOp4(v, OP_VOpen, iCur, 0, 0,
                        (const char*)pTab->pVtab, P4_VTAB);
    }else
#endif
    if( (pLevel->wsFlags & WHERE_IDX_ONLY)==0 ){
      int op = pWInfo->okOnePass ? OP_OpenWrite : OP_OpenRead;
      sqlite3OpenTable(pParse, pTabItem->iCursor, iDb, pTab, op);
      if( !pWInfo->okOnePass && pTab->nCol<BMS ){
        Bitmask b = pTabItem->colUsed;
        int n = 0;
        for(; b; b=b>>1, n++){}
        sqlite3VdbeChangeP2(v, sqlite3VdbeCurrentAddr(v)-2, n);
        assert( n<=pTab->nCol );
      }
    }else{
      sqlite3TableLock(pParse, iDb, pTab->tnum, 0, pTab->zName);
    }
    pLevel->iTabCur = pTabItem->iCursor;

    if( (pIx = pLevel->pIdx)!=0 ){
      KeyInfo *pKey = sqlite3IndexKeyinfo(pParse, pIx);

      assert( pIx->pSchema==pTab->pSchema );

      sqlite3VdbeAddOp2(v, OP_SetNumColumns, 0, pIx->nColumn+1);
      sqlite3VdbeAddOp4(v, OP_OpenRead, iIdxCur, pIx->tnum, iDb,
                        (char*)pKey, P4_KEYINFO_HANDOFF);
      VdbeComment((v, "%s", pIx->zName));
    }
    sqlite3CodeVerifySchema(pParse, iDb);
  }
................................................................................
  pWInfo->iTop = sqlite3VdbeCurrentAddr(v);

  /* Generate the code to do the search.  Each iteration of the for
  ** loop below generates code for a single nested loop of the VM
  ** program.
  */
  notReady = ~(Bitmask)0;
  for(i=0, pLevel=pWInfo->a; i<pTabList->nSrc; i++, pLevel++){
    int j, k;
    int iCur = pTabItem->iCursor;  /* The VDBE cursor for the table */
    Index *pIdx;       /* The index we will be using */
    int addrNxt;           /* Where to jump to continue with the next IN case */
    int iIdxCur;       /* The VDBE cursor for the index */
    int omitTable;     /* True if we use the index only */
    int bRev;          /* True if we need to scan in reverse order */

    pTabItem = &pTabList->a[pLevel->iFrom];
    iCur = pTabItem->iCursor;
    pIdx = pLevel->pIdx;
    iIdxCur = pLevel->iIdxCur;
    bRev = (pLevel->wsFlags & WHERE_REVERSE)!=0;
    omitTable = (pLevel->wsFlags & WHERE_IDX_ONLY)!=0;

    /* Create labels for the "break" and "continue" instructions
    ** for the current loop.  Jump to addrBrk to break out of a loop.
    ** Jump to cont to go immediately to the next iteration of the
    ** loop.
    **
    ** When there is an IN operator, we also have a "addrNxt" label that
    ** means to continue with the next IN value combination.  When
    ** there are no IN operators in the constraints, the "addrNxt" label
    ** is the same as "addrBrk".
    */
    addrBrk = pLevel->addrBrk = pLevel->addrNxt = sqlite3VdbeMakeLabel(v);
    addrCont = pLevel->addrCont = sqlite3VdbeMakeLabel(v);

    /* If this is the right table of a LEFT OUTER JOIN, allocate and
    ** initialize a memory cell that records if this table matches any
    ** row of the left table of the join.
    */
    if( pLevel->iFrom>0 && (pTabItem[0].jointype & JT_LEFT)!=0 ){
      pLevel->iLeftJoin = ++pParse->nMem;
      sqlite3VdbeAddOp2(v, OP_Integer, 0, pLevel->iLeftJoin);
      VdbeComment((v, "init LEFT JOIN no-match flag"));
    }

#ifndef SQLITE_OMIT_VIRTUALTABLE
    if( pLevel->pBestIdx ){
      /* Case 0:  The table is a virtual-table.  Use the VFilter and VNext
      **          to access the data.
      */
      int iReg;   /* P3 Value for OP_VFilter */
      sqlite3_index_info *pBestIdx = pLevel->pBestIdx;
      int nConstraint = pBestIdx->nConstraint;
      struct sqlite3_index_constraint_usage *aUsage =
                                                  pBestIdx->aConstraintUsage;
      const struct sqlite3_index_constraint *aConstraint =
                                                  pBestIdx->aConstraint;

      iReg = sqlite3GetTempRange(pParse, nConstraint+2);
      pParse->disableColCache++;
      for(j=1; j<=nConstraint; j++){
        for(k=0; k<nConstraint; k++){
          if( aUsage[k].argvIndex==j ){
            int iTerm = aConstraint[k].iTermOffset;
            assert( pParse->disableColCache );
            sqlite3ExprCode(pParse, wc.a[iTerm].pExpr->pRight, iReg+j+1);
            break;
          }
        }
        if( k==nConstraint ) break;
      }
      assert( pParse->disableColCache );
      pParse->disableColCache--;
      sqlite3VdbeAddOp2(v, OP_Integer, pBestIdx->idxNum, iReg);
      sqlite3VdbeAddOp2(v, OP_Integer, j-1, iReg+1);
      sqlite3VdbeAddOp4(v, OP_VFilter, iCur, addrBrk, iReg, pBestIdx->idxStr,
                        pBestIdx->needToFreeIdxStr ? P4_MPRINTF : P4_STATIC);
      sqlite3ReleaseTempRange(pParse, iReg, nConstraint+2);
      pBestIdx->needToFreeIdxStr = 0;
      for(j=0; j<nConstraint; j++){
        if( aUsage[j].omit ){
          int iTerm = aConstraint[j].iTermOffset;
          disableTerm(pLevel, &wc.a[iTerm]);
        }
      }
      pLevel->op = OP_VNext;
      pLevel->p1 = iCur;
      pLevel->p2 = sqlite3VdbeCurrentAddr(v);
    }else
#endif /* SQLITE_OMIT_VIRTUALTABLE */

    if( pLevel->wsFlags & WHERE_ROWID_EQ ){
      /* Case 1:  We can directly reference a single row using an
      **          equality comparison against the ROWID field.  Or
      **          we reference multiple rows using a "rowid IN (...)"
      **          construct.
      */
      int r1;
      int rtmp = sqlite3GetTempReg(pParse);
      pTerm = findTerm(&wc, iCur, -1, notReady, WO_EQ|WO_IN, 0);
      assert( pTerm!=0 );
      assert( pTerm->pExpr!=0 );
      assert( pTerm->leftCursor==iCur );
      assert( omitTable==0 );
      r1 = codeEqualityTerm(pParse, pTerm, pLevel, rtmp);
      addrNxt = pLevel->addrNxt;
      sqlite3VdbeAddOp2(v, OP_MustBeInt, r1, addrNxt);
      sqlite3VdbeAddOp3(v, OP_NotExists, iCur, addrNxt, r1);
      sqlite3ReleaseTempReg(pParse, rtmp);
      VdbeComment((v, "pk"));
      pLevel->op = OP_Noop;
    }else if( pLevel->wsFlags & WHERE_ROWID_RANGE ){
      /* Case 2:  We have an inequality comparison against the ROWID field.
      */
      int testOp = OP_Noop;
      int start;
      int memEndValue = 0;
      WhereTerm *pStart, *pEnd;

      assert( omitTable==0 );
      pStart = findTerm(&wc, iCur, -1, notReady, WO_GT|WO_GE, 0);
      pEnd = findTerm(&wc, iCur, -1, notReady, WO_LT|WO_LE, 0);
      if( bRev ){
        pTerm = pStart;
        pStart = pEnd;
        pEnd = pTerm;
      }
      if( pStart ){
        Expr *pX;             /* The expression that defines the start bound */
        int r1, rTemp;        /* Registers for holding the start boundary */

        /* The following constant maps TK_xx codes into corresponding 
        ** seek opcodes.  It depends on a particular ordering of TK_xx
        */
        const u8 aMoveOp[] = {
             /* TK_GT */  OP_SeekGt,
             /* TK_LE */  OP_SeekLe,
             /* TK_LT */  OP_SeekLt,
             /* TK_GE */  OP_SeekGe
        };
        assert( TK_LE==TK_GT+1 );      /* Make sure the ordering.. */
        assert( TK_LT==TK_GT+2 );      /*  ... of the TK_xx values... */
        assert( TK_GE==TK_GT+3 );      /*  ... is correcct. */

        pX = pStart->pExpr;
        assert( pX!=0 );
        assert( pStart->leftCursor==iCur );
        r1 = sqlite3ExprCodeTemp(pParse, pX->pRight, &rTemp);
        sqlite3VdbeAddOp3(v, aMoveOp[pX->op-TK_GT], iCur, addrBrk, r1);
        VdbeComment((v, "pk"));
        sqlite3ExprCacheAffinityChange(pParse, r1, 1);
        sqlite3ReleaseTempReg(pParse, rTemp);
        disableTerm(pLevel, pStart);
      }else{
        sqlite3VdbeAddOp2(v, bRev ? OP_Last : OP_Rewind, iCur, addrBrk);
      }
      if( pEnd ){
        Expr *pX;
        pX = pEnd->pExpr;
        assert( pX!=0 );
        assert( pEnd->leftCursor==iCur );
        memEndValue = ++pParse->nMem;
        sqlite3ExprCode(pParse, pX->pRight, memEndValue);
        if( pX->op==TK_LT || pX->op==TK_GT ){
          testOp = bRev ? OP_Le : OP_Ge;
        }else{
          testOp = bRev ? OP_Lt : OP_Gt;
        }
        disableTerm(pLevel, pEnd);
      }
      start = sqlite3VdbeCurrentAddr(v);
      pLevel->op = bRev ? OP_Prev : OP_Next;
      pLevel->p1 = iCur;
      pLevel->p2 = start;
      if( testOp!=OP_Noop ){
        int r1 = sqlite3GetTempReg(pParse);
        sqlite3VdbeAddOp2(v, OP_Rowid, iCur, r1);
        sqlite3VdbeAddOp3(v, testOp, memEndValue, addrBrk, r1);
        sqlite3VdbeChangeP5(v, SQLITE_AFF_NUMERIC | SQLITE_JUMPIFNULL);
        sqlite3ReleaseTempReg(pParse, r1);
      }
    }else if( pLevel->wsFlags & (WHERE_COLUMN_RANGE|WHERE_COLUMN_EQ) ){
      /* Case 3: A scan using an index.
      **
      **         The WHERE clause may contain zero or more equality 
      **         terms ("==" or "IN" operators) that refer to the N
      **         left-most columns of the index. It may also contain
      **         inequality constraints (>, <, >= or <=) on the indexed
      **         column that immediately follows the N equalities. Only 
      **         the right-most column can be an inequality - the rest must
      **         use the "==" and "IN" operators. For example, if the 
      **         index is on (x,y,z), then the following clauses are all 
      **         optimized:
      **
      **            x=5
      **            x=5 AND y=10
      **            x=5 AND y<10
      **            x=5 AND y>5 AND y<10
      **            x=5 AND y=5 AND z<=10
      **
      **         The z<10 term of the following cannot be used, only
      **         the x=5 term:
      **
      **            x=5 AND z<10
      **
      **         N may be zero if there are inequality constraints.
      **         If there are no inequality constraints, then N is at
      **         least one.
      **
      **         This case is also used when there are no WHERE clause
      **         constraints but an index is selected anyway, in order
      **         to force the output order to conform to an ORDER BY.
      */  
      int aStartOp[] = {
        0,
        0,
        OP_Rewind,           /* 2: (!start_constraints && startEq &&  !bRev) */
        OP_Last,             /* 3: (!start_constraints && startEq &&   bRev) */
        OP_SeekGt,           /* 4: (start_constraints  && !startEq && !bRev) */
        OP_SeekLt,           /* 5: (start_constraints  && !startEq &&  bRev) */
        OP_SeekGe,           /* 6: (start_constraints  &&  startEq && !bRev) */
        OP_SeekLe            /* 7: (start_constraints  &&  startEq &&  bRev) */
      };
      int aEndOp[] = {
        OP_Noop,             /* 0: (!end_constraints) */
        OP_IdxGE,            /* 1: (end_constraints && !bRev) */
        OP_IdxLT             /* 2: (end_constraints && bRev) */
      };
      int nEq = pLevel->nEq;
      int isMinQuery = 0;          /* If this is an optimized SELECT min(x).. */
      int regBase;                 /* Base register holding constraint values */
      int r1;                      /* Temp register */
      WhereTerm *pRangeStart = 0;  /* Inequality constraint at range start */
      WhereTerm *pRangeEnd = 0;    /* Inequality constraint at range end */
      int startEq;                 /* True if range start uses ==, >= or <= */
      int endEq;                   /* True if range end uses ==, >= or <= */
      int start_constraints;       /* Start of range is constrained */
      int nConstraint;             /* Number of constraint terms */
      int op;

      k = pIdx->aiColumn[nEq];     /* Column for inequality constraints */

      /* Generate code to evaluate all constraint terms using == or IN
      ** and store the values of those terms in an array of registers
      ** starting at regBase.
      */
      regBase = codeAllEqualityTerms(pParse, pLevel, &wc, notReady, 2);
      addrNxt = pLevel->addrNxt;

      /* If this loop satisfies a sort order (pOrderBy) request that 
      ** was passed to this function to implement a "SELECT min(x) ..." 
      ** query, then the caller will only allow the loop to run for
      ** a single iteration. This means that the first row returned
      ** should not have a NULL value stored in 'x'. If column 'x' is
      ** the first one after the nEq equality constraints in the index,
      ** this requires some special handling.
      */
      if( (wctrlFlags&WHERE_ORDERBY_MIN)!=0
       && (pLevel->wsFlags&WHERE_ORDERBY)
       && (pIdx->nColumn>nEq)
      ){
        assert( pOrderBy->nExpr==1 );
        assert( pOrderBy->a[0].pExpr->iColumn==pIdx->aiColumn[nEq] );
        isMinQuery = 1;
      }

      /* Find any inequality constraint terms for the start and end 
      ** of the range. 
      */
      if( pLevel->wsFlags & WHERE_TOP_LIMIT ){
        pRangeEnd = findTerm(&wc, iCur, k, notReady, (WO_LT|WO_LE), pIdx);
      }
      if( pLevel->wsFlags & WHERE_BTM_LIMIT ){
        pRangeStart = findTerm(&wc, iCur, k, notReady, (WO_GT|WO_GE), pIdx);
      }

      /* If we are doing a reverse order scan on an ascending index, or
      ** a forward order scan on a descending index, interchange the 
      ** start and end terms (pRangeStart and pRangeEnd).
      */
      if( bRev==(pIdx->aSortOrder[nEq]==SQLITE_SO_ASC) ){
        SWAP(WhereTerm *, pRangeEnd, pRangeStart);
      }

      testcase( pRangeStart && pRangeStart->eOperator & WO_LE );
      testcase( pRangeStart && pRangeStart->eOperator & WO_GE );
      testcase( pRangeEnd && pRangeEnd->eOperator & WO_LE );
      testcase( pRangeEnd && pRangeEnd->eOperator & WO_GE );
      startEq = !pRangeStart || pRangeStart->eOperator & (WO_LE|WO_GE);
      endEq =   !pRangeEnd || pRangeEnd->eOperator & (WO_LE|WO_GE);
      start_constraints = pRangeStart || nEq>0;

      /* Seek the index cursor to the start of the range. */
      nConstraint = nEq;
      if( pRangeStart ){
        int dcc = pParse->disableColCache;
        if( pRangeEnd ){
          pParse->disableColCache++;
        }
        sqlite3ExprCode(pParse, pRangeStart->pExpr->pRight, regBase+nEq);
        pParse->disableColCache = dcc;
        sqlite3VdbeAddOp2(v, OP_IsNull, regBase+nEq, addrNxt);
        nConstraint++;
      }else if( isMinQuery ){
        sqlite3VdbeAddOp2(v, OP_Null, 0, regBase+nEq);
        nConstraint++;
        startEq = 0;
        start_constraints = 1;
      }
      codeApplyAffinity(pParse, regBase, nConstraint, pIdx);
      op = aStartOp[(start_constraints<<2) + (startEq<<1) + bRev];
      assert( op!=0 );
      testcase( op==OP_Rewind );
      testcase( op==OP_Last );
      testcase( op==OP_SeekGt );
      testcase( op==OP_SeekGe );
      testcase( op==OP_SeekLe );
      testcase( op==OP_SeekLt );
      sqlite3VdbeAddOp4(v, op, iIdxCur, addrNxt, regBase, 
                        SQLITE_INT_TO_PTR(nConstraint), P4_INT32);

      /* Load the value for the inequality constraint at the end of the
      ** range (if any).
      */
      nConstraint = nEq;
      if( pRangeEnd ){
        sqlite3ExprCode(pParse, pRangeEnd->pExpr->pRight, regBase+nEq);
        sqlite3VdbeAddOp2(v, OP_IsNull, regBase+nEq, addrNxt);
        codeApplyAffinity(pParse, regBase, nEq+1, pIdx);
        nConstraint++;
      }

      /* Top of the loop body */
      pLevel->p2 = sqlite3VdbeCurrentAddr(v);

      /* Check if the index cursor is past the end of the range. */
      op = aEndOp[(pRangeEnd || nEq) * (1 + bRev)];
      testcase( op==OP_Noop );
      testcase( op==OP_IdxGE );
      testcase( op==OP_IdxLT );
      sqlite3VdbeAddOp4(v, op, iIdxCur, addrNxt, regBase,
                        SQLITE_INT_TO_PTR(nConstraint), P4_INT32);
      sqlite3VdbeChangeP5(v, endEq!=bRev ?1:0);

      /* If there are inequality constraints, check that the value
      ** of the table column that the inequality contrains is not NULL.
      ** If it is, jump to the next iteration of the loop.
      */
      r1 = sqlite3GetTempReg(pParse);
      testcase( pLevel->wsFlags & WHERE_BTM_LIMIT );
      testcase( pLevel->wsFlags & WHERE_TOP_LIMIT );
      if( pLevel->wsFlags & (WHERE_BTM_LIMIT|WHERE_TOP_LIMIT) ){
        sqlite3VdbeAddOp3(v, OP_Column, iIdxCur, nEq, r1);
        sqlite3VdbeAddOp2(v, OP_IsNull, r1, addrCont);
      }

      /* Seek the table cursor, if required */
      if( !omitTable ){
        sqlite3VdbeAddOp2(v, OP_IdxRowid, iIdxCur, r1);
        sqlite3VdbeAddOp2(v, OP_Seek, iCur, r1);  /* Deferred seek */
      }
      sqlite3ReleaseTempReg(pParse, r1);

      /* Record the instruction used to terminate the loop. Disable 
      ** WHERE clause terms made redundant by the index range scan.
      */
      pLevel->op = bRev ? OP_Prev : OP_Next;
      pLevel->p1 = iIdxCur;
      disableTerm(pLevel, pRangeStart);
      disableTerm(pLevel, pRangeEnd);
    }else if( pLevel->wsFlags & WHERE_MULTI_OR ){
      /* Case 4:  Two or more separately indexed terms connected by OR
      **
      ** Example:
      **
      **   CREATE TABLE t1(a,b,c,d);
      **   CREATE INDEX i1 ON t1(a);
      **   CREATE INDEX i2 ON t1(b);
      **   CREATE INDEX i3 ON t1(c);
      **
      **   SELECT * FROM t1 WHERE a=5 OR b=7 OR (c=11 AND d=13)
      **
      ** In the example, there are three indexed terms connected by OR.
      ** The top of the loop is constructed by creating a RowSet object
      ** and populating it.  Then looping over elements of the rowset.
      **
      **        Null 1
      **        # fill RowSet 1 with entries where a=5 using i1
      **        # fill Rowset 1 with entries where b=7 using i2
      **        # fill Rowset 1 with entries where c=11 and d=13 i3 and t1
      **     A: RowSetRead 1, B, 2
      **        Seek       i, 2
      **
      ** The bottom of the loop looks like this:
      **
      **     C: Goto       0, A
      **     B:
      */
    }else{
      /* Case 5:  There is no usable index.  We must do a complete
      **          scan of the entire table.
      */
      assert( omitTable==0 );
      assert( bRev==0 );
      pLevel->op = OP_Next;
      pLevel->p1 = iCur;
      pLevel->p2 = 1 + sqlite3VdbeAddOp2(v, OP_Rewind, iCur, addrBrk);
      pLevel->p5 = SQLITE_STMTSTATUS_FULLSCAN_STEP;
    }
    notReady &= ~getMask(&maskSet, iCur);

    /* Insert code to test every subexpression that can be completely
    ** computed using the current set of tables.
    */
    k = 0;
    for(pTerm=wc.a, j=wc.nTerm; j>0; j--, pTerm++){
      Expr *pE;
      testcase( pTerm->wtFlags & TERM_VIRTUAL );
      testcase( pTerm->wtFlags & TERM_CODED );
      if( pTerm->wtFlags & (TERM_VIRTUAL|TERM_CODED) ) continue;
      if( (pTerm->prereqAll & notReady)!=0 ) continue;
      pE = pTerm->pExpr;
      assert( pE!=0 );
      if( pLevel->iLeftJoin && !ExprHasProperty(pE, EP_FromJoin) ){
        continue;
      }
      pParse->disableColCache += k;
      sqlite3ExprIfFalse(pParse, pE, addrCont, SQLITE_JUMPIFNULL);
      pParse->disableColCache -= k;
      k = 1;
      pTerm->wtFlags |= TERM_CODED;
    }

    /* For a LEFT OUTER JOIN, generate code that will record the fact that
    ** at least one row of the right table has matched the left table.  
    */
    if( pLevel->iLeftJoin ){
      pLevel->addrFirst = sqlite3VdbeCurrentAddr(v);
      sqlite3VdbeAddOp2(v, OP_Integer, 1, pLevel->iLeftJoin);
      VdbeComment((v, "record LEFT JOIN hit"));
      sqlite3ExprClearColumnCache(pParse, pLevel->iTabCur);
      sqlite3ExprClearColumnCache(pParse, pLevel->iIdxCur);
      for(pTerm=wc.a, j=0; j<wc.nTerm; j++, pTerm++){
        testcase( pTerm->wtFlags & TERM_VIRTUAL );
        testcase( pTerm->wtFlags & TERM_CODED );
        if( pTerm->wtFlags & (TERM_VIRTUAL|TERM_CODED) ) continue;
        if( (pTerm->prereqAll & notReady)!=0 ) continue;
        assert( pTerm->pExpr );
        sqlite3ExprIfFalse(pParse, pTerm->pExpr, addrCont, SQLITE_JUMPIFNULL);
        pTerm->wtFlags |= TERM_CODED;
      }
    }
  }


#ifdef SQLITE_TEST  /* For testing and debugging use only */
  /* Record in the query plan information about the current table
  ** and the index used to access it (if any).  If the table itself
  ** is not used, its name is just '{}'.  If no index is used
  ** the index is listed as "{}".  If the primary key is used the
  ** index name is '*'.
................................................................................
    int n;
    pLevel = &pWInfo->a[i];
    pTabItem = &pTabList->a[pLevel->iFrom];
    z = pTabItem->zAlias;
    if( z==0 ) z = pTabItem->pTab->zName;
    n = sqlite3Strlen30(z);
    if( n+nQPlan < sizeof(sqlite3_query_plan)-10 ){
      if( pLevel->wsFlags & WHERE_IDX_ONLY ){
        memcpy(&sqlite3_query_plan[nQPlan], "{}", 2);
        nQPlan += 2;
      }else{
        memcpy(&sqlite3_query_plan[nQPlan], z, n);
        nQPlan += n;
      }
      sqlite3_query_plan[nQPlan++] = ' ';
    }
    testcase( pLevel->wsFlags & WHERE_ROWID_EQ );
    testcase( pLevel->wsFlags & WHERE_ROWID_RANGE );
    if( pLevel->wsFlags & (WHERE_ROWID_EQ|WHERE_ROWID_RANGE) ){
      memcpy(&sqlite3_query_plan[nQPlan], "* ", 2);
      nQPlan += 2;
    }else if( pLevel->pIdx==0 ){
      memcpy(&sqlite3_query_plan[nQPlan], "{} ", 3);
      nQPlan += 3;
    }else{
      n = sqlite3Strlen30(pLevel->pIdx->zName);
      if( n+nQPlan < sizeof(sqlite3_query_plan)-2 ){
        memcpy(&sqlite3_query_plan[nQPlan], pLevel->pIdx->zName, n);
        nQPlan += n;
        sqlite3_query_plan[nQPlan++] = ' ';
      }



    }
  }
  while( nQPlan>0 && sqlite3_query_plan[nQPlan-1]==' ' ){
    sqlite3_query_plan[--nQPlan] = 0;
  }
  sqlite3_query_plan[nQPlan] = 0;
  nQPlan = 0;
#endif /* SQLITE_TEST // Testing and debugging use only */

  /* Record the continuation address in the WhereInfo structure.  Then
  ** clean up and return.
  */
  pWInfo->iContinue = addrCont;
  whereClauseClear(&wc);
  return pWInfo;

  /* Jump here if malloc fails */
whereBeginError:
  whereClauseClear(&wc);
  whereInfoFree(db, pWInfo);
  return 0;
}

/*
** Generate the end of the WHERE loop.  See comments on 
** sqlite3WhereBegin() for additional information.
................................................................................
  for(i=pTabList->nSrc-1; i>=0; i--){
    pLevel = &pWInfo->a[i];
    sqlite3VdbeResolveLabel(v, pLevel->addrCont);
    if( pLevel->op!=OP_Noop ){
      sqlite3VdbeAddOp2(v, pLevel->op, pLevel->p1, pLevel->p2);
      sqlite3VdbeChangeP5(v, pLevel->p5);
    }
    if( pLevel->nIn ){
      struct InLoop *pIn;
      int j;
      sqlite3VdbeResolveLabel(v, pLevel->addrNxt);
      for(j=pLevel->nIn, pIn=&pLevel->aInLoop[j-1]; j>0; j--, pIn--){
        sqlite3VdbeJumpHere(v, pIn->addrInTop+1);
        sqlite3VdbeAddOp2(v, OP_Next, pIn->iCur, pIn->addrInTop);
        sqlite3VdbeJumpHere(v, pIn->addrInTop-1);
      }
      sqlite3DbFree(db, pLevel->aInLoop);
    }
    sqlite3VdbeResolveLabel(v, pLevel->addrBrk);
    if( pLevel->iLeftJoin ){
      int addr;
      addr = sqlite3VdbeAddOp1(v, OP_IfPos, pLevel->iLeftJoin);
      sqlite3VdbeAddOp1(v, OP_NullRow, pTabList->a[i].iCursor);
      if( pLevel->iIdxCur>=0 ){
................................................................................
  /* Close all of the cursors that were opened by sqlite3WhereBegin.
  */
  for(i=0, pLevel=pWInfo->a; i<pTabList->nSrc; i++, pLevel++){
    struct SrcList_item *pTabItem = &pTabList->a[pLevel->iFrom];
    Table *pTab = pTabItem->pTab;
    assert( pTab!=0 );
    if( (pTab->tabFlags & TF_Ephemeral)!=0 || pTab->pSelect ) continue;
    if( !pWInfo->okOnePass && (pLevel->wsFlags & WHERE_IDX_ONLY)==0 ){
      sqlite3VdbeAddOp1(v, OP_Close, pTabItem->iCursor);
    }
    if( pLevel->pIdx!=0 ){
      sqlite3VdbeAddOp1(v, OP_Close, pLevel->iIdxCur);
    }

    /* If this scan uses an index, make code substitutions to read data
    ** from the index in preference to the table. Sometimes, this means
    ** the table need never be read from. This is a performance boost,
    ** as the vdbe level waits until the table is read before actually
................................................................................
    ** 
    ** Calls to the code generator in between sqlite3WhereBegin and
    ** sqlite3WhereEnd will have created code that references the table
    ** directly.  This loop scans all that code looking for opcodes
    ** that reference the table and converts them into opcodes that
    ** reference the index.
    */
    if( pLevel->pIdx ){
      int k, j, last;
      VdbeOp *pOp;
      Index *pIdx = pLevel->pIdx;
      int useIndexOnly = pLevel->wsFlags & WHERE_IDX_ONLY;

      assert( pIdx!=0 );
      pOp = sqlite3VdbeGetOp(v, pWInfo->iTop);
      last = sqlite3VdbeCurrentAddr(v);
      for(k=pWInfo->iTop; k<last; k++, pOp++){
        if( pOp->p1!=pLevel->iTabCur ) continue;
        if( pOp->opcode==OP_Column ){







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802
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822
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....
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....
1928
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1936
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1951

1952
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1958
....
2040
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2073
....
2097
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2100
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2102
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2109
2110
2111
2112
2113
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2133
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2136
2137
....
2138
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2161
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2165
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2168
2169
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2171
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2174
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2178
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2209
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2240
2241
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2250
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2257
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2260
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2321
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2641
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....
2662
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2675
2676
....
2766
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2773

2774
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....
2789
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2796
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....
2837
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....
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** This module contains C code that generates VDBE code used to process
** the WHERE clause of SQL statements.  This module is responsible for
** generating the code that loops through a table looking for applicable
** rows.  Indices are selected and used to speed the search when doing
** so is applicable.  Because this module is responsible for selecting
** indices, you might also think of this module as the "query optimizer".
**
** $Id: where.c,v 1.340 2008/12/21 03:51:16 drh Exp $
*/
#include "sqliteInt.h"

/*
** Trace output macros
*/
#if defined(SQLITE_TEST) || defined(SQLITE_DEBUG)
int sqlite3WhereTrace = 0;
#endif
#if 1
# define WHERETRACE(X)  if(sqlite3WhereTrace) sqlite3DebugPrintf X
#else
# define WHERETRACE(X)
#endif

/* Forward reference
*/
typedef struct WhereClause WhereClause;
typedef struct WhereMaskSet WhereMaskSet;
typedef struct WhereOrInfo WhereOrInfo;
typedef struct WhereAndInfo WhereAndInfo;
typedef struct WhereCost WhereCost;

/*
** The query generator uses an array of instances of this structure to
** help it analyze the subexpressions of the WHERE clause.  Each WHERE
** clause subexpression is separated from the others by AND operators.
** (Note: the same data structure is also reused to hold a group of terms
** separated by OR operators.  But at the top-level, everything is AND
................................................................................
**
** If a term in the WHERE clause does not match either of the two previous
** categories, then eOperator==0.  The WhereTerm.pExpr field is still set
** to the original subexpression content and wtFlags is set up appropriately
** but no other fields in the WhereTerm object are meaningful.
**
** When eOperator!=0, prereqRight and prereqAll record sets of cursor numbers,
** but they do so indirectly.  A single WhereMaskSet structure translates
** cursor number into bits and the translated bit is stored in the prereq
** fields.  The translation is used in order to maximize the number of
** bits that will fit in a Bitmask.  The VDBE cursor numbers might be
** spread out over the non-negative integers.  For example, the cursor
** numbers might be 3, 8, 9, 10, 20, 23, 41, and 45.  The WhereMaskSet
** translates these sparse cursor numbers into consecutive integers
** beginning with 0 in order to make the best possible use of the available
** bits in the Bitmask.  So, in the example above, the cursor numbers
** would be mapped into integers 0 through 7.
**
** The number of terms in a join is limited by the number of bits
** in prereqRight and prereqAll.  The default is 64 bits, hence SQLite
................................................................................

/*
** An instance of the following structure holds all information about a
** WHERE clause.  Mostly this is a container for one or more WhereTerms.
*/
struct WhereClause {
  Parse *pParse;           /* The parser context */
  WhereMaskSet *pMaskSet;  /* Mapping of table cursor numbers to bitmasks */
  int nTerm;               /* Number of terms */
  int nSlot;               /* Number of entries in a[] */
  WhereTerm *a;            /* Each a[] describes a term of the WHERE cluase */
  WhereTerm aStatic[4];    /* Initial static space for a[] */
};

/*
** A WhereTerm with eOperator==WO_OR has its u.pOrInfo pointer set to
** a dynamically allocated instance of the following structure.
*/
struct WhereOrInfo {
  WhereClause wc;          /* Decomposition into subterms */
  Bitmask indexable;       /* Bitmask of all indexable tables in the clause */
  WherePlan *aPlan;        /* Search plan for each subterm */
};

/*
** A WhereTerm with eOperator==WO_AND has its u.pAndInfo pointer set to
** a dynamically allocated instance of the following structure.
*/
struct WhereAndInfo {
................................................................................
** SrcList_item.iCursor and Expr.iTable fields.  For any given WHERE 
** clause, the cursor numbers might not begin with 0 and they might
** contain gaps in the numbering sequence.  But we want to make maximum
** use of the bits in our bitmasks.  This structure provides a mapping
** from the sparse cursor numbers into consecutive integers beginning
** with 0.
**
** If WhereMaskSet.ix[A]==B it means that The A-th bit of a Bitmask
** corresponds VDBE cursor number B.  The A-th bit of a bitmask is 1<<A.
**
** For example, if the WHERE clause expression used these VDBE
** cursors:  4, 5, 8, 29, 57, 73.  Then the  WhereMaskSet structure
** would map those cursor numbers into bits 0 through 5.
**
** Note that the mapping is not necessarily ordered.  In the example
** above, the mapping might go like this:  4->3, 5->1, 8->2, 29->0,
** 57->5, 73->4.  Or one of 719 other combinations might be used. It
** does not really matter.  What is important is that sparse cursor
** numbers all get mapped into bit numbers that begin with 0 and contain
** no gaps.
*/
struct WhereMaskSet {
  int n;                        /* Number of assigned cursor values */
  int ix[BMS];                  /* Cursor assigned to each bit */
};

/*
** A WhereCost object records a lookup strategy and the estimated
** cost of pursuing that strategy.
*/
struct WhereCost {
  WherePlan plan;    /* The lookup strategy */
  double rCost;      /* Overall cost of pursuing this search strategy */
  double nRow;       /* Estimated number of output rows */
};

/*
** Bitmasks for the operators that indices are able to exploit.  An
** OR-ed combination of these values can be used when searching for
** terms in the where clause.
*/
#define WO_IN     0x001
................................................................................
** join.  Tickets #2177 and #2189.
*/
#define WHERE_ROWID_EQ     0x00001000  /* rowid=EXPR or rowid IN (...) */
#define WHERE_ROWID_RANGE  0x00002000  /* rowid<EXPR and/or rowid>EXPR */
#define WHERE_COLUMN_EQ    0x00010000  /* x=EXPR or x IN (...) */
#define WHERE_COLUMN_RANGE 0x00020000  /* x<EXPR and/or x>EXPR */
#define WHERE_COLUMN_IN    0x00040000  /* x IN (...) */
#define WHERE_INDEXED      0x00070000  /* Anything that uses an index */
#define WHERE_IN_ABLE      0x00071000  /* Able to support an IN operator */
#define WHERE_TOP_LIMIT    0x00100000  /* x<EXPR or x<=EXPR constraint */
#define WHERE_BTM_LIMIT    0x00200000  /* x>EXPR or x>=EXPR constraint */
#define WHERE_IDX_ONLY     0x00800000  /* Use index only - omit table */
#define WHERE_ORDERBY      0x01000000  /* Output will appear in correct order */
#define WHERE_REVERSE      0x02000000  /* Scan in reverse order */
#define WHERE_UNIQUE       0x04000000  /* Selects no more than one row */
#define WHERE_VIRTUALTABLE 0x08000000  /* Use virtual-table processing */
................................................................................

/*
** Initialize a preallocated WhereClause structure.
*/
static void whereClauseInit(
  WhereClause *pWC,        /* The WhereClause to be initialized */
  Parse *pParse,           /* The parsing context */
  WhereMaskSet *pMaskSet   /* Mapping from table cursor numbers to bitmasks */
){
  pWC->pParse = pParse;
  pWC->pMaskSet = pMaskSet;
  pWC->nTerm = 0;
  pWC->nSlot = ArraySize(pWC->aStatic);
  pWC->a = pWC->aStatic;
}
................................................................................

/*
** Deallocate all memory associated with a WhereOrInfo object.
*/
static void whereOrInfoDelete(sqlite3 *db, WhereOrInfo *p){
  if( p ){
    whereClauseClear(&p->wc);
    sqlite3DbFree(db, p->aPlan);
    sqlite3DbFree(db, p);
  }
}

/*
** Deallocate all memory associated with a WhereAndInfo object.
*/
................................................................................
*/
#define initMaskSet(P)  memset(P, 0, sizeof(*P))

/*
** Return the bitmask for the given cursor number.  Return 0 if
** iCursor is not in the set.
*/
static Bitmask getMask(WhereMaskSet *pMaskSet, int iCursor){
  int i;
  for(i=0; i<pMaskSet->n; i++){
    if( pMaskSet->ix[i]==iCursor ){
      return ((Bitmask)1)<<i;
    }
  }
  return 0;
................................................................................
** Create a new mask for cursor iCursor.
**
** There is one cursor per table in the FROM clause.  The number of
** tables in the FROM clause is limited by a test early in the
** sqlite3WhereBegin() routine.  So we know that the pMaskSet->ix[]
** array will never overflow.
*/
static void createMask(WhereMaskSet *pMaskSet, int iCursor){
  assert( pMaskSet->n < ArraySize(pMaskSet->ix) );
  pMaskSet->ix[pMaskSet->n++] = iCursor;
}

/*
** This routine walks (recursively) an expression tree and generates
** a bitmask indicating which tables are used in that expression
................................................................................
** the header comment on that routine for additional information.
** The sqlite3ResolveExprNames() routines looks for column names and
** sets their opcodes to TK_COLUMN and their Expr.iTable fields to
** the VDBE cursor number of the table.  This routine just has to
** translate the cursor numbers into bitmask values and OR all
** the bitmasks together.
*/
static Bitmask exprListTableUsage(WhereMaskSet*, ExprList*);
static Bitmask exprSelectTableUsage(WhereMaskSet*, Select*);
static Bitmask exprTableUsage(WhereMaskSet *pMaskSet, Expr *p){
  Bitmask mask = 0;
  if( p==0 ) return 0;
  if( p->op==TK_COLUMN ){
    mask = getMask(pMaskSet, p->iTable);
    return mask;
  }
  mask = exprTableUsage(pMaskSet, p->pRight);
  mask |= exprTableUsage(pMaskSet, p->pLeft);
  mask |= exprListTableUsage(pMaskSet, p->pList);
  mask |= exprSelectTableUsage(pMaskSet, p->pSelect);
  return mask;
}
static Bitmask exprListTableUsage(WhereMaskSet *pMaskSet, ExprList *pList){
  int i;
  Bitmask mask = 0;
  if( pList ){
    for(i=0; i<pList->nExpr; i++){
      mask |= exprTableUsage(pMaskSet, pList->a[i].pExpr);
    }
  }
  return mask;
}
static Bitmask exprSelectTableUsage(WhereMaskSet *pMaskSet, Select *pS){
  Bitmask mask = 0;
  while( pS ){
    mask |= exprListTableUsage(pMaskSet, pS->pEList);
    mask |= exprListTableUsage(pMaskSet, pS->pGroupBy);
    mask |= exprListTableUsage(pMaskSet, pS->pOrderBy);
    mask |= exprTableUsage(pMaskSet, pS->pWhere);
    mask |= exprTableUsage(pMaskSet, pS->pHaving);
................................................................................
  WhereClause *pWC,         /* the complete WHERE clause */
  int idxTerm               /* Index of the OR-term to be analyzed */
){
  Parse *pParse = pWC->pParse;            /* Parser context */
  sqlite3 *db = pParse->db;               /* Database connection */
  WhereTerm *pTerm = &pWC->a[idxTerm];    /* The term to be analyzed */
  Expr *pExpr = pTerm->pExpr;             /* The expression of the term */
  WhereMaskSet *pMaskSet = pWC->pMaskSet; /* Table use masks */
  int i;                                  /* Loop counters */
  WhereClause *pOrWc;       /* Breakup of pTerm into subterms */
  WhereTerm *pOrTerm;       /* A Sub-term within the pOrWc */
  WhereOrInfo *pOrInfo;     /* Additional information associated with pTerm */
  Bitmask chngToIN;         /* Tables that might satisfy case 1 */
  Bitmask indexable;        /* Tables that are indexable, satisfying case 2 */

................................................................................
  assert( (pTerm->wtFlags & (TERM_DYNAMIC|TERM_ORINFO|TERM_ANDINFO))==0 );
  assert( pExpr->op==TK_OR );
  pTerm->u.pOrInfo = pOrInfo = sqlite3DbMallocRaw(db, sizeof(*pOrInfo));
  if( pOrInfo==0 ) return;
  pTerm->wtFlags |= TERM_ORINFO;
  pOrWc = &pOrInfo->wc;
  whereClauseInit(pOrWc, pWC->pParse, pMaskSet);
  pOrInfo->aPlan = 0;
  whereSplit(pOrWc, pExpr, TK_OR);
  exprAnalyzeAll(pSrc, pOrWc);
  if( db->mallocFailed ) return;
  assert( pOrWc->nTerm>=2 );

  /*
  ** Compute the set of tables that might satisfy cases 1 or 2.
................................................................................
        chngToIN &= b;
      }
    }
  }

  /*
  ** Record the set of tables that satisfy case 2.  The set might be
  ** empty.
  */
  pOrInfo->indexable = indexable;
  pTerm->eOperator = indexable==0 ? 0 : WO_OR;

  /*
  ** chngToIN holds a set of tables that *might* satisfy case 1.  But
  ** we have to do some additional checking to see if case 1 really
  ** is satisfied.
  */
  if( chngToIN ){
................................................................................
        pTerm->nChild = 1;
      }else{
        sqlite3ExprListDelete(db, pList);
      }
      pTerm->eOperator = 0;  /* case 1 trumps case 2 */
    }
  }

  /* If case 2 applies, allocate space for pOrInfo->aPlan
  */
  if( pTerm->eOperator==WO_OR ){
    pOrInfo->aPlan = sqlite3DbMallocRaw(db, pOrWc->nTerm*sizeof(WherePlan));
  }
}
#endif /* !SQLITE_OMIT_OR_OPTIMIZATION && !SQLITE_OMIT_SUBQUERY */


/*
** The input to this routine is an WhereTerm structure with only the
** "pExpr" field filled in.  The job of this routine is to analyze the
................................................................................
*/
static void exprAnalyze(
  SrcList *pSrc,            /* the FROM clause */
  WhereClause *pWC,         /* the WHERE clause */
  int idxTerm               /* Index of the term to be analyzed */
){
  WhereTerm *pTerm;                /* The term to be analyzed */
  WhereMaskSet *pMaskSet;          /* Set of table index masks */
  Expr *pExpr;                     /* The expression to be analyzed */
  Bitmask prereqLeft;              /* Prerequesites of the pExpr->pLeft */
  Bitmask prereqAll;               /* Prerequesites of pExpr */
  Bitmask extraRight = 0;
  int nPattern;
  int isComplete;
  int noCase;
................................................................................

/*
** Return TRUE if any of the expressions in pList->a[iFirst...] contain
** a reference to any table other than the iBase table.
*/
static int referencesOtherTables(
  ExprList *pList,          /* Search expressions in ths list */
  WhereMaskSet *pMaskSet,   /* Mapping from tables to bitmaps */
  int iFirst,               /* Be searching with the iFirst-th expression */
  int iBase                 /* Ignore references to this table */
){
  Bitmask allowed = ~getMask(pMaskSet, iBase);
  while( iFirst<pList->nExpr ){
    if( (exprTableUsage(pMaskSet, pList->a[iFirst++].pExpr)&allowed)!=0 ){
      return 1;
................................................................................
** ASC or DESC.  (Terms of the ORDER BY clause past the end of a UNIQUE
** index do not need to satisfy this constraint.)  The *pbRev value is
** set to 1 if the ORDER BY clause is all DESC and it is set to 0 if
** the ORDER BY clause is all ASC.
*/
static int isSortingIndex(
  Parse *pParse,          /* Parsing context */
  WhereMaskSet *pMaskSet, /* Mapping from table cursor numbers to bitmaps */
  Index *pIdx,            /* The index we are testing */
  int base,               /* Cursor number for the table to be sorted */
  ExprList *pOrderBy,     /* The ORDER BY clause */
  int nEqCol,             /* Number of index columns with == constraints */
  int *pbRev              /* Set to 1 if ORDER BY is DESC */
){
  int i, j;                       /* Loop counters */
................................................................................
** Check table to see if the ORDER BY clause in pOrderBy can be satisfied
** by sorting in order of ROWID.  Return true if so and set *pbRev to be
** true for reverse ROWID and false for forward ROWID order.
*/
static int sortableByRowid(
  int base,               /* Cursor number for table to be sorted */
  ExprList *pOrderBy,     /* The ORDER BY clause */
  WhereMaskSet *pMaskSet, /* Mapping from table cursors to bitmaps */
  int *pbRev              /* Set to 1 if ORDER BY is DESC */
){
  Expr *p;

  assert( pOrderBy!=0 );
  assert( pOrderBy->nExpr>0 );
  p = pOrderBy->a[0].pExpr;
................................................................................

  *(int*)&pIdxInfo->nOrderBy = nOrderBy;
  return pIdxInfo->estimatedCost;
}
#endif /* SQLITE_OMIT_VIRTUALTABLE */

/*
** Find the query plan for accessing a particular table.  Write the
** best query plan and its cost into the WhereCost object supplied as the
** last parameter.
**
** The lowest cost plan wins.  The cost is an estimate of the amount of
** CPU and disk I/O need to process the request using the selected plan.
** Factors that influence cost include:
**
**    *  The estimated number of rows that will be retrieved.  (The
**       fewer the better.)
**
**    *  Whether or not sorting must occur.
**
**    *  Whether or not there must be separate lookups in the
**       index and in the main table.
**
** If there was an INDEXED BY clause attached to the table in the SELECT
** statement, then this function only considers plans using the 
** named index. If one cannot be found, then the returned cost is
** SQLITE_BIG_DBL. If a plan can be found that uses the named index, 
** then the cost is calculated in the usual way.
**
** If a NOT INDEXED clause was attached to the table in the SELECT 
** statement, then no indexes are considered. However, the selected 
** plan may still take advantage of the tables built-in rowid
** index.
*/
static void bestIndex(
  Parse *pParse,              /* The parsing context */
  WhereClause *pWC,           /* The WHERE clause */
  struct SrcList_item *pSrc,  /* The FROM clause term to search */
  Bitmask notReady,           /* Mask of cursors that are not available */
  ExprList *pOrderBy,         /* The ORDER BY clause */
  WhereCost *pCost            /* Lowest cost query plan */


){
  WhereTerm *pTerm;           /* A single term of the WHERE clause */




  int iCur = pSrc->iCursor;   /* The cursor of the table to be accessed */
  Index *pProbe;              /* An index we are evaluating */
  int rev;                    /* True to scan in reverse order */
  int wsFlags;                /* Flags associated with pProbe */
  int nEq;                    /* Number of == or IN constraints */
  int eqTermMask;             /* Mask of valid equality operators */
  double cost;                /* Cost of using pProbe */
  double nRow;                /* Estimated number of rows in result set */

  WHERETRACE(("bestIndex: tbl=%s notReady=%llx\n", pSrc->pTab->zName,notReady));

  pProbe = pSrc->pTab->pIndex;
  if( pSrc->notIndexed ){
    pProbe = 0;
  }

  /* If the table has no indices and there are no terms in the where
  ** clause that refer to the ROWID, then we will never be able to do
  ** anything other than a full table scan on this table.  We might as
  ** well put it first in the join order.  That way, perhaps it can be
  ** referenced by other tables in the join.
  */
  memset(pCost, 0, sizeof(*pCost));
  if( pProbe==0 &&
     findTerm(pWC, iCur, -1, 0, WO_EQ|WO_IN|WO_LT|WO_LE|WO_GT|WO_GE,0)==0 &&
     (pOrderBy==0 || !sortableByRowid(iCur, pOrderBy, pWC->pMaskSet, &rev)) ){



    return;
  }
  pCost->rCost = SQLITE_BIG_DBL;

  /* Check for a rowid=EXPR or rowid IN (...) constraints. If there was
  ** an INDEXED BY clause attached to this table, skip this step.
  */
  if( !pSrc->pIndex ){
    pTerm = findTerm(pWC, iCur, -1, notReady, WO_EQ|WO_IN, 0);
    if( pTerm ){
      Expr *pExpr;

      pCost->plan.wsFlags = WHERE_ROWID_EQ;
      if( pTerm->eOperator & WO_EQ ){
        /* Rowid== is always the best pick.  Look no further.  Because only
        ** a single row is generated, output is always in sorted order */
        pCost->plan.wsFlags = WHERE_ROWID_EQ | WHERE_UNIQUE;
        pCost->plan.nEq = 1;
        WHERETRACE(("... best is rowid\n"));
        pCost->rCost = 0;
        pCost->nRow = 1;
        return;
      }else if( (pExpr = pTerm->pExpr)->pList!=0 ){
        /* Rowid IN (LIST): cost is NlogN where N is the number of list
        ** elements.  */
        pCost->rCost = pCost->nRow = pExpr->pList->nExpr;
        pCost->rCost *= estLog(pCost->rCost);
      }else{
        /* Rowid IN (SELECT): cost is NlogN where N is the number of rows
        ** in the result of the inner select.  We have no way to estimate
        ** that value so make a wild guess. */
        pCost->nRow = 100;
        pCost->rCost = 200;
      }
      WHERETRACE(("... rowid IN cost: %.9g\n", pCost->rCost));
    }
  
    /* Estimate the cost of a table scan.  If we do not know how many
    ** entries are in the table, use 1 million as a guess.
    */
    cost = pProbe ? pProbe->aiRowEst[0] : 1000000;
    WHERETRACE(("... table scan base cost: %.9g\n", cost));
................................................................................
        wsFlags |= WHERE_BTM_LIMIT;
        cost /= 3;  /* Guess that rowid>EXPR eliminates two-thirds of rows */
      }
      WHERETRACE(("... rowid range reduces cost to %.9g\n", cost));
    }else{
      wsFlags = 0;
    }
    nRow = cost;
  
    /* If the table scan does not satisfy the ORDER BY clause, increase
    ** the cost by NlogN to cover the expense of sorting. */
    if( pOrderBy ){
      if( sortableByRowid(iCur, pOrderBy, pWC->pMaskSet, &rev) ){
        wsFlags |= WHERE_ORDERBY|WHERE_ROWID_RANGE;
        if( rev ){
................................................................................
          wsFlags |= WHERE_REVERSE;
        }
      }else{
        cost += cost*estLog(cost);
        WHERETRACE(("... sorting increases cost to %.9g\n", cost));
      }
    }
    if( cost<pCost->rCost ){
      pCost->rCost = cost;
      pCost->nRow = nRow;
      pCost->plan.wsFlags = wsFlags;
    }
  }

  /* If the pSrc table is the right table of a LEFT JOIN then we may not
  ** use an index to satisfy IS NULL constraints on that table.  This is
  ** because columns might end up being NULL if the table does not match -
  ** a circumstance which the index cannot help us discover.  Ticket #2177.
................................................................................
        if( pExpr->pSelect!=0 ){
          inMultiplier *= 25;
        }else if( ALWAYS(pExpr->pList) ){
          inMultiplier *= pExpr->pList->nExpr + 1;
        }
      }
    }
    nRow = pProbe->aiRowEst[i] * inMultiplier;
    cost = nRow * estLog(inMultiplier);
    nEq = i;
    if( pProbe->onError!=OE_None && (wsFlags & WHERE_COLUMN_IN)==0
         && nEq==pProbe->nColumn ){
      wsFlags |= WHERE_UNIQUE;
    }
    WHERETRACE(("...... nEq=%d inMult=%.9g cost=%.9g\n",nEq,inMultiplier,cost));

................................................................................
      int j = pProbe->aiColumn[nEq];
      pTerm = findTerm(pWC, iCur, j, notReady, WO_LT|WO_LE|WO_GT|WO_GE, pProbe);
      if( pTerm ){
        wsFlags |= WHERE_COLUMN_RANGE;
        if( findTerm(pWC, iCur, j, notReady, WO_LT|WO_LE, pProbe) ){
          wsFlags |= WHERE_TOP_LIMIT;
          cost /= 3;
          nRow /= 3;
        }
        if( findTerm(pWC, iCur, j, notReady, WO_GT|WO_GE, pProbe) ){
          wsFlags |= WHERE_BTM_LIMIT;
          cost /= 3;
          nRow /= 3;
        }
        WHERETRACE(("...... range reduces cost to %.9g\n", cost));
      }
    }

    /* Add the additional cost of sorting if that is a factor.
    */
................................................................................
        cost /= 2;
        WHERETRACE(("...... idx-only reduces cost to %.9g\n", cost));
      }
    }

    /* If this index has achieved the lowest cost so far, then use it.
    */
    if( wsFlags!=0 && cost < pCost->rCost ){

      pCost->rCost = cost;
      pCost->nRow = nRow;
      pCost->plan.wsFlags = wsFlags;
      pCost->plan.nEq = nEq;
      assert( pCost->plan.wsFlags & WHERE_INDEXED );
      pCost->plan.u.pIdx = pProbe;
    }
  }

  /* Report the best result
  */
  pCost->plan.wsFlags |= eqTermMask;
  WHERETRACE(("best index is %s, cost=%.9g, nrow=%.9g, wsFlags=%x, nEq=%d\n",
        (pCost->plan.wsFlags & WHERE_INDEXED)!=0 ?
             pCost->plan.u.pIdx->zName : "(none)", pCost->nRow,

        pCost->rCost, pCost->plan.wsFlags, pCost->plan.nEq));

}


/*
** Disable a term in the WHERE clause.  Except, do not disable the term
** if it controls a LEFT OUTER JOIN and it did not originate in the ON
** or USING clause of that join.
................................................................................

    assert( pX->op==TK_IN );
    iReg = iTarget;
    eType = sqlite3FindInIndex(pParse, pX, 0);
    iTab = pX->iTable;
    sqlite3VdbeAddOp2(v, OP_Rewind, iTab, 0);
    VdbeComment((v, "%.*s", pX->span.n, pX->span.z));
    assert( pLevel->plan.wsFlags & WHERE_IN_ABLE );
    if( pLevel->u.in.nIn==0 ){
      pLevel->addrNxt = sqlite3VdbeMakeLabel(v);
    }
    pLevel->u.in.nIn++;
    pLevel->u.in.aInLoop =
       sqlite3DbReallocOrFree(pParse->db, pLevel->u.in.aInLoop,
                              sizeof(pLevel->u.in.aInLoop[0])*pLevel->u.in.nIn);
    pIn = pLevel->u.in.aInLoop;
    if( pIn ){
      pIn += pLevel->u.in.nIn - 1;
      pIn->iCur = iTab;
      if( eType==IN_INDEX_ROWID ){
        pIn->addrInTop = sqlite3VdbeAddOp2(v, OP_Rowid, iTab, iReg);
      }else{
        pIn->addrInTop = sqlite3VdbeAddOp3(v, OP_Column, iTab, 0, iReg);
      }
      sqlite3VdbeAddOp1(v, OP_IsNull, iReg);
    }else{
      pLevel->u.in.nIn = 0;
    }
#endif
  }
  disableTerm(pLevel, pTerm);
  return iReg;
}

................................................................................
static int codeAllEqualityTerms(
  Parse *pParse,        /* Parsing context */
  WhereLevel *pLevel,   /* Which nested loop of the FROM we are coding */
  WhereClause *pWC,     /* The WHERE clause */
  Bitmask notReady,     /* Which parts of FROM have not yet been coded */
  int nExtraReg         /* Number of extra registers to allocate */
){
  int nEq = pLevel->plan.nEq;   /* The number of == or IN constraints to code */
  Vdbe *v = pParse->pVdbe;      /* The vm under construction */
  Index *pIdx;                  /* The index being used for this loop */
  int iCur = pLevel->iTabCur;   /* The cursor of the table */
  WhereTerm *pTerm;             /* A single constraint term */
  int j;                        /* Loop counter */
  int regBase;                  /* Base register */

  /* This module is only called on query plans that use an index. */
  assert( pLevel->plan.wsFlags & WHERE_INDEXED );
  pIdx = pLevel->plan.u.pIdx;

  /* Figure out how many memory cells we will need then allocate them.
  ** We always need at least one used to store the loop terminator
  ** value.  If there are IN operators we'll need one for each == or
  ** IN constraint.
  */
  regBase = pParse->nMem + 1;
  pParse->nMem += pLevel->plan.nEq + 1 + nExtraReg;

  /* Evaluate the equality constraints
  */
  assert( pIdx->nColumn>=nEq );
  for(j=0; j<nEq; j++){
    int r1;
    int k = pIdx->aiColumn[j];
    pTerm = findTerm(pWC, iCur, k, notReady, pLevel->plan.wsFlags, pIdx);
    if( NEVER(pTerm==0) ) break;
    assert( (pTerm->wtFlags & TERM_CODED)==0 );
    r1 = codeEqualityTerm(pParse, pTerm, pLevel, regBase+j);
    if( r1!=regBase+j ){
      sqlite3VdbeAddOp2(v, OP_SCopy, r1, regBase+j);
    }
    testcase( pTerm->eOperator & WO_ISNULL );
................................................................................
    testcase( pTerm->eOperator & WO_IN );
    if( (pTerm->eOperator & (WO_ISNULL|WO_IN))==0 ){
      sqlite3VdbeAddOp2(v, OP_IsNull, regBase+j, pLevel->addrBrk);
    }
  }
  return regBase;
}

/*
** Generate code for the start of the iLevel-th loop in the WHERE clause
** implementation described by pWInfo.
*/
static Bitmask codeOneLoopStart(
  WhereInfo *pWInfo,   /* Complete information about the WHERE clause */
  int iLevel,          /* Which level of pWInfo->a[] should be coded */
  u8 wctrlFlags,       /* One of the WHERE_* flags defined in sqliteInt.h */
  Bitmask notReady     /* Which tables are currently available */
){
  int j, k;            /* Loop counters */
  int iCur;            /* The VDBE cursor for the table */
  int addrNxt;         /* Where to jump to continue with the next IN case */
  int omitTable;       /* True if we use the index only */
  int bRev;            /* True if we need to scan in reverse order */
  WhereLevel *pLevel;  /* The where level to be coded */
  WhereClause *pWC;    /* Decomposition of the entire WHERE clause */
  WhereTerm *pTerm;               /* A WHERE clause term */
  Parse *pParse;                  /* Parsing context */
  Vdbe *v;                        /* The prepared stmt under constructions */
  struct SrcList_item *pTabItem;  /* FROM clause term being coded */
  int addrBrk;
  int addrCont;
  

  pParse = pWInfo->pParse;
  v = pParse->pVdbe;
  pWC = pWInfo->pWC;
  pLevel = &pWInfo->a[iLevel];
  pTabItem = &pWInfo->pTabList->a[pLevel->iFrom];
  iCur = pTabItem->iCursor;
  bRev = (pLevel->plan.wsFlags & WHERE_REVERSE)!=0;
  omitTable = (pLevel->plan.wsFlags & WHERE_IDX_ONLY)!=0;

  /* Create labels for the "break" and "continue" instructions
  ** for the current loop.  Jump to addrBrk to break out of a loop.
  ** Jump to cont to go immediately to the next iteration of the
  ** loop.
  **
  ** When there is an IN operator, we also have a "addrNxt" label that
  ** means to continue with the next IN value combination.  When
  ** there are no IN operators in the constraints, the "addrNxt" label
  ** is the same as "addrBrk".
  */
  addrBrk = pLevel->addrBrk = pLevel->addrNxt = sqlite3VdbeMakeLabel(v);
  addrCont = pLevel->addrCont = sqlite3VdbeMakeLabel(v);

  /* If this is the right table of a LEFT OUTER JOIN, allocate and
  ** initialize a memory cell that records if this table matches any
  ** row of the left table of the join.
  */
  if( pLevel->iFrom>0 && (pTabItem[0].jointype & JT_LEFT)!=0 ){
    pLevel->iLeftJoin = ++pParse->nMem;
    sqlite3VdbeAddOp2(v, OP_Integer, 0, pLevel->iLeftJoin);
    VdbeComment((v, "init LEFT JOIN no-match flag"));
  }

#ifndef SQLITE_OMIT_VIRTUALTABLE
  if(  (pLevel->plan.wsFlags & WHERE_VIRTUALTABLE)!=0 ){
    /* Case 0:  The table is a virtual-table.  Use the VFilter and VNext
    **          to access the data.
    */
    int iReg;   /* P3 Value for OP_VFilter */
    sqlite3_index_info *pVtabIdx = pLevel->plan.u.pVtabIdx;
    int nConstraint = pVtabIdx->nConstraint;
    struct sqlite3_index_constraint_usage *aUsage =
                                                pVtabIdx->aConstraintUsage;
    const struct sqlite3_index_constraint *aConstraint =
                                                pVtabIdx->aConstraint;

    iReg = sqlite3GetTempRange(pParse, nConstraint+2);
    pParse->disableColCache++;
    for(j=1; j<=nConstraint; j++){
      for(k=0; k<nConstraint; k++){
        if( aUsage[k].argvIndex==j ){
          int iTerm = aConstraint[k].iTermOffset;
          assert( pParse->disableColCache );
          sqlite3ExprCode(pParse, pWC->a[iTerm].pExpr->pRight, iReg+j+1);
          break;
        }
      }
      if( k==nConstraint ) break;
    }
    assert( pParse->disableColCache );
    pParse->disableColCache--;
    sqlite3VdbeAddOp2(v, OP_Integer, pVtabIdx->idxNum, iReg);
    sqlite3VdbeAddOp2(v, OP_Integer, j-1, iReg+1);
    sqlite3VdbeAddOp4(v, OP_VFilter, iCur, addrBrk, iReg, pVtabIdx->idxStr,
                      pVtabIdx->needToFreeIdxStr ? P4_MPRINTF : P4_STATIC);
    sqlite3ReleaseTempRange(pParse, iReg, nConstraint+2);
    pVtabIdx->needToFreeIdxStr = 0;
    for(j=0; j<nConstraint; j++){
      if( aUsage[j].omit ){
        int iTerm = aConstraint[j].iTermOffset;
        disableTerm(pLevel, &pWC->a[iTerm]);
      }
    }
    pLevel->op = OP_VNext;
    pLevel->p1 = iCur;
    pLevel->p2 = sqlite3VdbeCurrentAddr(v);
  }else
#endif /* SQLITE_OMIT_VIRTUALTABLE */

  if( pLevel->plan.wsFlags & WHERE_ROWID_EQ ){
    /* Case 1:  We can directly reference a single row using an
    **          equality comparison against the ROWID field.  Or
    **          we reference multiple rows using a "rowid IN (...)"
    **          construct.
    */
    int r1;
    int rtmp = sqlite3GetTempReg(pParse);
    pTerm = findTerm(pWC, iCur, -1, notReady, WO_EQ|WO_IN, 0);
    assert( pTerm!=0 );
    assert( pTerm->pExpr!=0 );
    assert( pTerm->leftCursor==iCur );
    assert( omitTable==0 );
    r1 = codeEqualityTerm(pParse, pTerm, pLevel, rtmp);
    addrNxt = pLevel->addrNxt;
    sqlite3VdbeAddOp2(v, OP_MustBeInt, r1, addrNxt);
    sqlite3VdbeAddOp3(v, OP_NotExists, iCur, addrNxt, r1);
    sqlite3ReleaseTempReg(pParse, rtmp);
    VdbeComment((v, "pk"));
    pLevel->op = OP_Noop;
  }else if( pLevel->plan.wsFlags & WHERE_ROWID_RANGE ){
    /* Case 2:  We have an inequality comparison against the ROWID field.
    */
    int testOp = OP_Noop;
    int start;
    int memEndValue = 0;
    WhereTerm *pStart, *pEnd;

    assert( omitTable==0 );
    pStart = findTerm(pWC, iCur, -1, notReady, WO_GT|WO_GE, 0);
    pEnd = findTerm(pWC, iCur, -1, notReady, WO_LT|WO_LE, 0);
    if( bRev ){
      pTerm = pStart;
      pStart = pEnd;
      pEnd = pTerm;
    }
    if( pStart ){
      Expr *pX;             /* The expression that defines the start bound */
      int r1, rTemp;        /* Registers for holding the start boundary */

      /* The following constant maps TK_xx codes into corresponding 
      ** seek opcodes.  It depends on a particular ordering of TK_xx
      */
      const u8 aMoveOp[] = {
           /* TK_GT */  OP_SeekGt,
           /* TK_LE */  OP_SeekLe,
           /* TK_LT */  OP_SeekLt,
           /* TK_GE */  OP_SeekGe
      };
      assert( TK_LE==TK_GT+1 );      /* Make sure the ordering.. */
      assert( TK_LT==TK_GT+2 );      /*  ... of the TK_xx values... */
      assert( TK_GE==TK_GT+3 );      /*  ... is correcct. */

      pX = pStart->pExpr;
      assert( pX!=0 );
      assert( pStart->leftCursor==iCur );
      r1 = sqlite3ExprCodeTemp(pParse, pX->pRight, &rTemp);
      sqlite3VdbeAddOp3(v, aMoveOp[pX->op-TK_GT], iCur, addrBrk, r1);
      VdbeComment((v, "pk"));
      sqlite3ExprCacheAffinityChange(pParse, r1, 1);
      sqlite3ReleaseTempReg(pParse, rTemp);
      disableTerm(pLevel, pStart);
    }else{
      sqlite3VdbeAddOp2(v, bRev ? OP_Last : OP_Rewind, iCur, addrBrk);
    }
    if( pEnd ){
      Expr *pX;
      pX = pEnd->pExpr;
      assert( pX!=0 );
      assert( pEnd->leftCursor==iCur );
      memEndValue = ++pParse->nMem;
      sqlite3ExprCode(pParse, pX->pRight, memEndValue);
      if( pX->op==TK_LT || pX->op==TK_GT ){
        testOp = bRev ? OP_Le : OP_Ge;
      }else{
        testOp = bRev ? OP_Lt : OP_Gt;
      }
      disableTerm(pLevel, pEnd);
    }
    start = sqlite3VdbeCurrentAddr(v);
    pLevel->op = bRev ? OP_Prev : OP_Next;
    pLevel->p1 = iCur;
    pLevel->p2 = start;
    if( testOp!=OP_Noop ){
      int r1 = sqlite3GetTempReg(pParse);
      sqlite3VdbeAddOp2(v, OP_Rowid, iCur, r1);
      sqlite3VdbeAddOp3(v, testOp, memEndValue, addrBrk, r1);
      sqlite3VdbeChangeP5(v, SQLITE_AFF_NUMERIC | SQLITE_JUMPIFNULL);
      sqlite3ReleaseTempReg(pParse, r1);
    }
  }else if( pLevel->plan.wsFlags & (WHERE_COLUMN_RANGE|WHERE_COLUMN_EQ) ){
    /* Case 3: A scan using an index.
    **
    **         The WHERE clause may contain zero or more equality 
    **         terms ("==" or "IN" operators) that refer to the N
    **         left-most columns of the index. It may also contain
    **         inequality constraints (>, <, >= or <=) on the indexed
    **         column that immediately follows the N equalities. Only 
    **         the right-most column can be an inequality - the rest must
    **         use the "==" and "IN" operators. For example, if the 
    **         index is on (x,y,z), then the following clauses are all 
    **         optimized:
    **
    **            x=5
    **            x=5 AND y=10
    **            x=5 AND y<10
    **            x=5 AND y>5 AND y<10
    **            x=5 AND y=5 AND z<=10
    **
    **         The z<10 term of the following cannot be used, only
    **         the x=5 term:
    **
    **            x=5 AND z<10
    **
    **         N may be zero if there are inequality constraints.
    **         If there are no inequality constraints, then N is at
    **         least one.
    **
    **         This case is also used when there are no WHERE clause
    **         constraints but an index is selected anyway, in order
    **         to force the output order to conform to an ORDER BY.
    */  
    int aStartOp[] = {
      0,
      0,
      OP_Rewind,           /* 2: (!start_constraints && startEq &&  !bRev) */
      OP_Last,             /* 3: (!start_constraints && startEq &&   bRev) */
      OP_SeekGt,           /* 4: (start_constraints  && !startEq && !bRev) */
      OP_SeekLt,           /* 5: (start_constraints  && !startEq &&  bRev) */
      OP_SeekGe,           /* 6: (start_constraints  &&  startEq && !bRev) */
      OP_SeekLe            /* 7: (start_constraints  &&  startEq &&  bRev) */
    };
    int aEndOp[] = {
      OP_Noop,             /* 0: (!end_constraints) */
      OP_IdxGE,            /* 1: (end_constraints && !bRev) */
      OP_IdxLT             /* 2: (end_constraints && bRev) */
    };
    int nEq = pLevel->plan.nEq;
    int isMinQuery = 0;          /* If this is an optimized SELECT min(x).. */
    int regBase;                 /* Base register holding constraint values */
    int r1;                      /* Temp register */
    WhereTerm *pRangeStart = 0;  /* Inequality constraint at range start */
    WhereTerm *pRangeEnd = 0;    /* Inequality constraint at range end */
    int startEq;                 /* True if range start uses ==, >= or <= */
    int endEq;                   /* True if range end uses ==, >= or <= */
    int start_constraints;       /* Start of range is constrained */
    int nConstraint;             /* Number of constraint terms */
    Index *pIdx;         /* The index we will be using */
    int iIdxCur;         /* The VDBE cursor for the index */
    int op;

    pIdx = pLevel->plan.u.pIdx;
    iIdxCur = pLevel->iIdxCur;
    k = pIdx->aiColumn[nEq];     /* Column for inequality constraints */

    /* Generate code to evaluate all constraint terms using == or IN
    ** and store the values of those terms in an array of registers
    ** starting at regBase.
    */
    regBase = codeAllEqualityTerms(pParse, pLevel, pWC, notReady, 2);
    addrNxt = pLevel->addrNxt;

    /* If this loop satisfies a sort order (pOrderBy) request that 
    ** was passed to this function to implement a "SELECT min(x) ..." 
    ** query, then the caller will only allow the loop to run for
    ** a single iteration. This means that the first row returned
    ** should not have a NULL value stored in 'x'. If column 'x' is
    ** the first one after the nEq equality constraints in the index,
    ** this requires some special handling.
    */
    if( (wctrlFlags&WHERE_ORDERBY_MIN)!=0
     && (pLevel->plan.wsFlags&WHERE_ORDERBY)
     && (pIdx->nColumn>nEq)
    ){
      /* assert( pOrderBy->nExpr==1 ); */
      /* assert( pOrderBy->a[0].pExpr->iColumn==pIdx->aiColumn[nEq] ); */
      isMinQuery = 1;
    }

    /* Find any inequality constraint terms for the start and end 
    ** of the range. 
    */
    if( pLevel->plan.wsFlags & WHERE_TOP_LIMIT ){
      pRangeEnd = findTerm(pWC, iCur, k, notReady, (WO_LT|WO_LE), pIdx);
    }
    if( pLevel->plan.wsFlags & WHERE_BTM_LIMIT ){
      pRangeStart = findTerm(pWC, iCur, k, notReady, (WO_GT|WO_GE), pIdx);
    }

    /* If we are doing a reverse order scan on an ascending index, or
    ** a forward order scan on a descending index, interchange the 
    ** start and end terms (pRangeStart and pRangeEnd).
    */
    if( bRev==(pIdx->aSortOrder[nEq]==SQLITE_SO_ASC) ){
      SWAP(WhereTerm *, pRangeEnd, pRangeStart);
    }

    testcase( pRangeStart && pRangeStart->eOperator & WO_LE );
    testcase( pRangeStart && pRangeStart->eOperator & WO_GE );
    testcase( pRangeEnd && pRangeEnd->eOperator & WO_LE );
    testcase( pRangeEnd && pRangeEnd->eOperator & WO_GE );
    startEq = !pRangeStart || pRangeStart->eOperator & (WO_LE|WO_GE);
    endEq =   !pRangeEnd || pRangeEnd->eOperator & (WO_LE|WO_GE);
    start_constraints = pRangeStart || nEq>0;

    /* Seek the index cursor to the start of the range. */
    nConstraint = nEq;
    if( pRangeStart ){
      int dcc = pParse->disableColCache;
      if( pRangeEnd ){
        pParse->disableColCache++;
      }
      sqlite3ExprCode(pParse, pRangeStart->pExpr->pRight, regBase+nEq);
      pParse->disableColCache = dcc;
      sqlite3VdbeAddOp2(v, OP_IsNull, regBase+nEq, addrNxt);
      nConstraint++;
    }else if( isMinQuery ){
      sqlite3VdbeAddOp2(v, OP_Null, 0, regBase+nEq);
      nConstraint++;
      startEq = 0;
      start_constraints = 1;
    }
    codeApplyAffinity(pParse, regBase, nConstraint, pIdx);
    op = aStartOp[(start_constraints<<2) + (startEq<<1) + bRev];
    assert( op!=0 );
    testcase( op==OP_Rewind );
    testcase( op==OP_Last );
    testcase( op==OP_SeekGt );
    testcase( op==OP_SeekGe );
    testcase( op==OP_SeekLe );
    testcase( op==OP_SeekLt );
    sqlite3VdbeAddOp4(v, op, iIdxCur, addrNxt, regBase, 
                      SQLITE_INT_TO_PTR(nConstraint), P4_INT32);

    /* Load the value for the inequality constraint at the end of the
    ** range (if any).
    */
    nConstraint = nEq;
    if( pRangeEnd ){
      sqlite3ExprCode(pParse, pRangeEnd->pExpr->pRight, regBase+nEq);
      sqlite3VdbeAddOp2(v, OP_IsNull, regBase+nEq, addrNxt);
      codeApplyAffinity(pParse, regBase, nEq+1, pIdx);
      nConstraint++;
    }

    /* Top of the loop body */
    pLevel->p2 = sqlite3VdbeCurrentAddr(v);

    /* Check if the index cursor is past the end of the range. */
    op = aEndOp[(pRangeEnd || nEq) * (1 + bRev)];
    testcase( op==OP_Noop );
    testcase( op==OP_IdxGE );
    testcase( op==OP_IdxLT );
    sqlite3VdbeAddOp4(v, op, iIdxCur, addrNxt, regBase,
                      SQLITE_INT_TO_PTR(nConstraint), P4_INT32);
    sqlite3VdbeChangeP5(v, endEq!=bRev ?1:0);

    /* If there are inequality constraints, check that the value
    ** of the table column that the inequality contrains is not NULL.
    ** If it is, jump to the next iteration of the loop.
    */
    r1 = sqlite3GetTempReg(pParse);
    testcase( pLevel->plan.wsFlags & WHERE_BTM_LIMIT );
    testcase( pLevel->plan.wsFlags & WHERE_TOP_LIMIT );
    if( pLevel->plan.wsFlags & (WHERE_BTM_LIMIT|WHERE_TOP_LIMIT) ){
      sqlite3VdbeAddOp3(v, OP_Column, iIdxCur, nEq, r1);
      sqlite3VdbeAddOp2(v, OP_IsNull, r1, addrCont);
    }

    /* Seek the table cursor, if required */
    if( !omitTable ){
      sqlite3VdbeAddOp2(v, OP_IdxRowid, iIdxCur, r1);
      sqlite3VdbeAddOp2(v, OP_Seek, iCur, r1);  /* Deferred seek */
    }
    sqlite3ReleaseTempReg(pParse, r1);

    /* Record the instruction used to terminate the loop. Disable 
    ** WHERE clause terms made redundant by the index range scan.
    */
    pLevel->op = bRev ? OP_Prev : OP_Next;
    pLevel->p1 = iIdxCur;
    disableTerm(pLevel, pRangeStart);
    disableTerm(pLevel, pRangeEnd);
  }else if( pLevel->plan.wsFlags & WHERE_MULTI_OR ){
    /* Case 4:  Two or more separately indexed terms connected by OR
    **
    ** Example:
    **
    **   CREATE TABLE t1(a,b,c,d);
    **   CREATE INDEX i1 ON t1(a);
    **   CREATE INDEX i2 ON t1(b);
    **   CREATE INDEX i3 ON t1(c);
    **
    **   SELECT * FROM t1 WHERE a=5 OR b=7 OR (c=11 AND d=13)
    **
    ** In the example, there are three indexed terms connected by OR.
    ** The top of the loop is constructed by creating a RowSet object
    ** and populating it.  Then looping over elements of the rowset.
    **
    **        Null 1
    **        # fill RowSet 1 with entries where a=5 using i1
    **        # fill Rowset 1 with entries where b=7 using i2
    **        # fill Rowset 1 with entries where c=11 and d=13 i3 and t1
    **     A: RowSetRead 1, B, 2
    **        Seek       i, 2
    **
    ** The bottom of the loop looks like this:
    **
    **        Goto       0, A
    **     B:
    */
    int regRowset;         /* Register holding the RowSet object */
    int regNextRowid;      /* Register holding next rowid */
    WhereTerm *pTerm;      /* The complete OR-clause */
    WhereClause *pOrWc;    /* The OR-clause broken out into subterms */
    WhereTerm *pOrTerm;    /* A single subterm within the OR-clause */
   
    pTerm = pLevel->plan.u.pTerm;
    assert( pTerm!=0 );
    assert( pTerm->eOperator==WO_OR );
    assert( (pTerm->wtFlags & TERM_ORINFO)!=0 );
    pOrWc = &pTerm->u.pOrInfo->wc;
    
    regRowset = sqlite3GetTempReg(pParse);
    sqlite3VdbeAddOp1(v, OP_Null, regRowset);
    for(j=0, pOrTerm=pOrWc->a; j<pOrWc->nTerm; j++, pOrTerm++){
      if( pOrTerm->leftCursor!=iCur ) continue;
      /* fillRowSetFromIdx(pParse, regRowset, pTabItem, pOrTerm); */
    }
    regNextRowid = sqlite3GetTempReg(pParse);
    sqlite3VdbeResolveLabel(v, addrCont);
    addrCont = 
       sqlite3VdbeAddOp3(v, OP_RowSetRead, regRowset, addrBrk, regNextRowid);
    sqlite3VdbeAddOp2(v, OP_Seek, iCur, regNextRowid);
    sqlite3ReleaseTempReg(pParse, regNextRowid);
    pLevel->op = OP_Goto;
    pLevel->p2 = addrCont;
  }else{
    /* Case 5:  There is no usable index.  We must do a complete
    **          scan of the entire table.
    */
    assert( omitTable==0 );
    assert( bRev==0 );
    pLevel->op = OP_Next;
    pLevel->p1 = iCur;
    pLevel->p2 = 1 + sqlite3VdbeAddOp2(v, OP_Rewind, iCur, addrBrk);
    pLevel->p5 = SQLITE_STMTSTATUS_FULLSCAN_STEP;
  }
  notReady &= ~getMask(pWC->pMaskSet, iCur);

  /* Insert code to test every subexpression that can be completely
  ** computed using the current set of tables.
  */
  k = 0;
  for(pTerm=pWC->a, j=pWC->nTerm; j>0; j--, pTerm++){
    Expr *pE;
    testcase( pTerm->wtFlags & TERM_VIRTUAL );
    testcase( pTerm->wtFlags & TERM_CODED );
    if( pTerm->wtFlags & (TERM_VIRTUAL|TERM_CODED) ) continue;
    if( (pTerm->prereqAll & notReady)!=0 ) continue;
    pE = pTerm->pExpr;
    assert( pE!=0 );
    if( pLevel->iLeftJoin && !ExprHasProperty(pE, EP_FromJoin) ){
      continue;
    }
    pParse->disableColCache += k;
    sqlite3ExprIfFalse(pParse, pE, addrCont, SQLITE_JUMPIFNULL);
    pParse->disableColCache -= k;
    k = 1;
    pTerm->wtFlags |= TERM_CODED;
  }

  /* For a LEFT OUTER JOIN, generate code that will record the fact that
  ** at least one row of the right table has matched the left table.  
  */
  if( pLevel->iLeftJoin ){
    pLevel->addrFirst = sqlite3VdbeCurrentAddr(v);
    sqlite3VdbeAddOp2(v, OP_Integer, 1, pLevel->iLeftJoin);
    VdbeComment((v, "record LEFT JOIN hit"));
    sqlite3ExprClearColumnCache(pParse, pLevel->iTabCur);
    sqlite3ExprClearColumnCache(pParse, pLevel->iIdxCur);
    for(pTerm=pWC->a, j=0; j<pWC->nTerm; j++, pTerm++){
      testcase( pTerm->wtFlags & TERM_VIRTUAL );
      testcase( pTerm->wtFlags & TERM_CODED );
      if( pTerm->wtFlags & (TERM_VIRTUAL|TERM_CODED) ) continue;
      if( (pTerm->prereqAll & notReady)!=0 ) continue;
      assert( pTerm->pExpr );
      sqlite3ExprIfFalse(pParse, pTerm->pExpr, addrCont, SQLITE_JUMPIFNULL);
      pTerm->wtFlags |= TERM_CODED;
    }
  }
  return notReady;
}

#if defined(SQLITE_TEST)
/*
** The following variable holds a text description of query plan generated
** by the most recent call to sqlite3WhereBegin().  Each call to WhereBegin
** overwrites the previous.  This information is used for testing and
** analysis only.
................................................................................
    for(i=0; i<pWInfo->nLevel; i++){
      sqlite3_index_info *pInfo = pWInfo->a[i].pIdxInfo;
      if( pInfo ){
        assert( pInfo->needToFreeIdxStr==0 );
        sqlite3DbFree(db, pInfo);
      }
    }
    whereClauseClear(pWInfo->pWC);
    sqlite3DbFree(db, pWInfo);
  }
}


/*
** Generate the beginning of the loop used for WHERE clause processing.
................................................................................
  Expr *pWhere,         /* The WHERE clause */
  ExprList **ppOrderBy, /* An ORDER BY clause, or NULL */
  u8 wctrlFlags         /* One of the WHERE_* flags defined in sqliteInt.h */
){
  int i;                     /* Loop counter */
  WhereInfo *pWInfo;         /* Will become the return value of this function */
  Vdbe *v = pParse->pVdbe;   /* The virtual database engine */

  Bitmask notReady;          /* Cursors that are not yet positioned */

  WhereMaskSet *pMaskSet;    /* The expression mask set */
  //WhereClause wc;          /* The WHERE clause is divided into these terms */
  WhereClause *pWC;               /* Decomposition of the WHERE clause */
  struct SrcList_item *pTabItem;  /* A single entry from pTabList */
  WhereLevel *pLevel;             /* A single level in the pWInfo list */
  int iFrom;                      /* First unused FROM clause element */
  int andFlags;              /* AND-ed combination of all pWC->a[].wtFlags */
  sqlite3 *db;               /* Database connection */
  ExprList *pOrderBy = 0;

  /* The number of tables in the FROM clause is limited by the number of
  ** bits in a Bitmask 
  */
  if( pTabList->nSrc>BMS ){
................................................................................
    return 0;
  }

  if( ppOrderBy ){
    pOrderBy = *ppOrderBy;
  }









  /* Allocate and initialize the WhereInfo structure that will become the
  ** return value.
  */
  db = pParse->db;
  pWInfo = sqlite3DbMallocZero(db,  
                      sizeof(WhereInfo)
                      + (pTabList->nSrc-1)*sizeof(WhereLevel)
                      + sizeof(WhereClause)
                      + sizeof(WhereMaskSet)
           );
  if( db->mallocFailed ){
    goto whereBeginError;
  }
  pWInfo->nLevel = pTabList->nSrc;
  pWInfo->pParse = pParse;
  pWInfo->pTabList = pTabList;
  pWInfo->iBreak = sqlite3VdbeMakeLabel(v);
  pWInfo->pWC = pWC = (WhereClause*)&pWInfo->a[pWInfo->nLevel];
  pMaskSet = (WhereMaskSet*)&pWC[1];

  /* Split the WHERE clause into separate subexpressions where each
  ** subexpression is separated by an AND operator.
  */
  initMaskSet(pMaskSet);
  whereClauseInit(pWC, pParse, pMaskSet);
  sqlite3ExprCodeConstants(pParse, pWhere);
  whereSplit(pWC, pWhere, TK_AND);
    
  /* Special case: a WHERE clause that is constant.  Evaluate the
  ** expression and either jump over all of the code or fall thru.
  */
  if( pWhere && (pTabList->nSrc==0 || sqlite3ExprIsConstantNotJoin(pWhere)) ){
    sqlite3ExprIfFalse(pParse, pWhere, pWInfo->iBreak, SQLITE_JUMPIFNULL);
    pWhere = 0;
  }
................................................................................
  ** is (X-1).   An expression from the ON clause of a LEFT JOIN can use
  ** its Expr.iRightJoinTable value to find the bitmask of the right table
  ** of the join.  Subtracting one from the right table bitmask gives a
  ** bitmask for all tables to the left of the join.  Knowing the bitmask
  ** for all tables to the left of a left join is important.  Ticket #3015.
  */
  for(i=0; i<pTabList->nSrc; i++){
    createMask(pMaskSet, pTabList->a[i].iCursor);
  }
#ifndef NDEBUG
  {
    Bitmask toTheLeft = 0;
    for(i=0; i<pTabList->nSrc; i++){
      Bitmask m = getMask(pMaskSet, pTabList->a[i].iCursor);
      assert( (m-1)==toTheLeft );
      toTheLeft |= m;
    }
  }
#endif

  /* Analyze all of the subexpressions.  Note that exprAnalyze() might
  ** add new virtual terms onto the end of the WHERE clause.  We do not
  ** want to analyze these virtual terms, so start analyzing at the end
  ** and work forward so that the added virtual terms are never processed.
  */
  exprAnalyzeAll(pTabList, pWC);
  if( db->mallocFailed ){
    goto whereBeginError;
  }

  /* Chose the best index to use for each table in the FROM clause.
  **
  ** This loop fills in the following fields:
................................................................................
  **
  **   pWInfo->a[].pIdx      The index to use for this level of the loop.
  **   pWInfo->a[].wsFlags   WHERE_xxx flags associated with pIdx
  **   pWInfo->a[].nEq       The number of == and IN constraints
  **   pWInfo->a[].iFrom     Which term of the FROM clause is being coded
  **   pWInfo->a[].iTabCur   The VDBE cursor for the database table
  **   pWInfo->a[].iIdxCur   The VDBE cursor for the index
  **   pWInfo->a[].pTerm     When wsFlags==WO_OR, the OR-clause term
  **
  ** This loop also figures out the nesting order of tables in the FROM
  ** clause.
  */
  notReady = ~(Bitmask)0;
  pTabItem = pTabList->a;
  pLevel = pWInfo->a;
  andFlags = ~0;
  WHERETRACE(("*** Optimizer Start ***\n"));
  for(i=iFrom=0, pLevel=pWInfo->a; i<pTabList->nSrc; i++, pLevel++){
    WhereCost bestPlan;         /* Most efficient plan seen so far */
    Index *pIdx;                /* Index for FROM table at pTabItem */



    int j;                      /* For looping over FROM tables */




    int bestJ = 0;              /* The value of j */
    Bitmask m;                  /* Bitmask value for j or bestJ */
    int once = 0;               /* True when first table is seen */


    memset(&bestPlan, 0, sizeof(bestPlan));
    bestPlan.rCost = SQLITE_BIG_DBL;
    for(j=iFrom, pTabItem=&pTabList->a[j]; j<pTabList->nSrc; j++, pTabItem++){
      int doNotReorder;  /* True if this table should not be reordered */
      WhereCost sCost;   /* Cost information from bestIndex() */

      doNotReorder =  (pTabItem->jointype & (JT_LEFT|JT_CROSS))!=0;
      if( once && doNotReorder ) break;
      m = getMask(pMaskSet, pTabItem->iCursor);
      if( (m & notReady)==0 ){
        if( j==iFrom ) iFrom++;
        continue;
      }
      assert( pTabItem->pTab );
#ifndef SQLITE_OMIT_VIRTUALTABLE
      if( IsVirtual(pTabItem->pTab) ){
        sqlite3_index_info *pVtabIdx; /* Current virtual index */
        sqlite3_index_info **ppIdxInfo = &pWInfo->a[j].pIdxInfo;
        sCost.rCost = bestVirtualIndex(pParse, pWC, pTabItem, notReady,
                                       ppOrderBy ? *ppOrderBy : 0, i==0,
                                       ppIdxInfo);
        sCost.plan.wsFlags = WHERE_VIRTUALTABLE;
        sCost.plan.u.pVtabIdx = pVtabIdx = *ppIdxInfo;
        if( pVtabIdx && pVtabIdx->orderByConsumed ){
          sCost.plan.wsFlags = WHERE_VIRTUALTABLE | WHERE_ORDERBY;
        }

        sCost.plan.nEq = 0;
        if( (SQLITE_BIG_DBL/2.0)<sCost.rCost ){
          /* The cost is not allowed to be larger than SQLITE_BIG_DBL (the
          ** inital value of lowestCost in this loop. If it is, then
          ** the (cost<lowestCost) test below will never be true.

          */ 
          sCost.rCost = (SQLITE_BIG_DBL/2.0);
        }
      }else 
#endif
      {
        bestIndex(pParse, pWC, pTabItem, notReady,
                  (i==0 && ppOrderBy) ? *ppOrderBy : 0, &sCost);


      }

      if( sCost.rCost<bestPlan.rCost ){
        once = 1;




        bestPlan = sCost;
        bestJ = j;

      }
      if( doNotReorder ) break;
    }
    WHERETRACE(("*** Optimizer selects table %d for loop %d\n", bestJ,
           pLevel-pWInfo->a));
    if( (bestPlan.plan.wsFlags & WHERE_ORDERBY)!=0 ){
      *ppOrderBy = 0;
    }
    andFlags &= bestPlan.plan.wsFlags;
    pLevel->plan = bestPlan.plan;
    if( bestPlan.plan.wsFlags & WHERE_INDEXED ){




      pLevel->iIdxCur = pParse->nTab++;
    }else{
      pLevel->iIdxCur = -1;
    }
    notReady &= ~getMask(pMaskSet, pTabList->a[bestJ].iCursor);
    pLevel->iFrom = bestJ;

    /* Check that if the table scanned by this loop iteration had an
    ** INDEXED BY clause attached to it, that the named index is being
    ** used for the scan. If not, then query compilation has failed.
    ** Return an error.
    */
    pIdx = pTabList->a[bestJ].pIndex;
    assert( !pIdx
           || (bestPlan.plan.wsFlags&WHERE_INDEXED)==0
           || pIdx==bestPlan.plan.u.pIdx );
    if( pIdx
     && ((bestPlan.plan.wsFlags & WHERE_INDEXED)==0
         || bestPlan.plan.u.pIdx!=pIdx)
    ){
      sqlite3ErrorMsg(pParse, "cannot use index: %s", pIdx->zName);
      goto whereBeginError;
    }
  }
  WHERETRACE(("*** Optimizer Finished ***\n"));

  /* If the total query only selects a single row, then the ORDER BY
................................................................................
  ** to use a one-pass algorithm, determine if this is appropriate.
  ** The one-pass algorithm only works if the WHERE clause constraints
  ** the statement to update a single row.
  */
  assert( (wctrlFlags & WHERE_ONEPASS_DESIRED)==0 || pWInfo->nLevel==1 );
  if( (wctrlFlags & WHERE_ONEPASS_DESIRED)!=0 && (andFlags & WHERE_UNIQUE)!=0 ){
    pWInfo->okOnePass = 1;
    pWInfo->a[0].plan.wsFlags &= ~WHERE_IDX_ONLY;
  }

  /* Open all tables in the pTabList and any indices selected for
  ** searching those tables.
  */
  sqlite3CodeVerifySchema(pParse, -1); /* Insert the cookie verifier Goto */
  for(i=0, pLevel=pWInfo->a; i<pTabList->nSrc; i++, pLevel++){
    Table *pTab;     /* Table to open */

    int iDb;         /* Index of database containing table/index */


#ifndef SQLITE_OMIT_EXPLAIN
    if( pParse->explain==2 ){
      char *zMsg;
      struct SrcList_item *pItem = &pTabList->a[pLevel->iFrom];
      zMsg = sqlite3MPrintf(db, "TABLE %s", pItem->zName);
      if( pItem->zAlias ){
        zMsg = sqlite3MAppendf(db, zMsg, "%s AS %s", zMsg, pItem->zAlias);
      }
      if( (pLevel->plan.wsFlags & WHERE_INDEXED)!=0 ){
        zMsg = sqlite3MAppendf(db, zMsg, "%s WITH INDEX %s",
           zMsg, pLevel->plan.u.pIdx->zName);
      }else if( pLevel->plan.wsFlags & (WHERE_ROWID_EQ|WHERE_ROWID_RANGE) ){
        zMsg = sqlite3MAppendf(db, zMsg, "%s USING PRIMARY KEY", zMsg);
      }
#ifndef SQLITE_OMIT_VIRTUALTABLE
      else if( (pLevel->plan.wsFlags & WHERE_VIRTUALTABLE)!=0 ){
        sqlite3_index_info *pVtabIdx = pLevel->plan.u.pVtabIdx;
        zMsg = sqlite3MAppendf(db, zMsg, "%s VIRTUAL TABLE INDEX %d:%s", zMsg,
                    pVtabIdx->idxNum, pVtabIdx->idxStr);
      }
#endif
      if( pLevel->plan.wsFlags & WHERE_ORDERBY ){
        zMsg = sqlite3MAppendf(db, zMsg, "%s ORDER BY", zMsg);
      }
      sqlite3VdbeAddOp4(v, OP_Explain, i, pLevel->iFrom, 0, zMsg, P4_DYNAMIC);
    }
#endif /* SQLITE_OMIT_EXPLAIN */
    pTabItem = &pTabList->a[pLevel->iFrom];
    pTab = pTabItem->pTab;
    iDb = sqlite3SchemaToIndex(pParse->db, pTab->pSchema);
    if( (pTab->tabFlags & TF_Ephemeral)!=0 || pTab->pSelect ) continue;
#ifndef SQLITE_OMIT_VIRTUALTABLE
    if( (pLevel->plan.wsFlags & WHERE_VIRTUALTABLE)!=0 ){
      int iCur = pTabItem->iCursor;
      sqlite3VdbeAddOp4(v, OP_VOpen, iCur, 0, 0,
                        (const char*)pTab->pVtab, P4_VTAB);
    }else
#endif
    if( (pLevel->plan.wsFlags & WHERE_IDX_ONLY)==0 ){
      int op = pWInfo->okOnePass ? OP_OpenWrite : OP_OpenRead;
      sqlite3OpenTable(pParse, pTabItem->iCursor, iDb, pTab, op);
      if( !pWInfo->okOnePass && pTab->nCol<BMS ){
        Bitmask b = pTabItem->colUsed;
        int n = 0;
        for(; b; b=b>>1, n++){}
        sqlite3VdbeChangeP2(v, sqlite3VdbeCurrentAddr(v)-2, n);
        assert( n<=pTab->nCol );
      }
    }else{
      sqlite3TableLock(pParse, iDb, pTab->tnum, 0, pTab->zName);
    }
    pLevel->iTabCur = pTabItem->iCursor;
    if( (pLevel->plan.wsFlags & WHERE_INDEXED)!=0 ){
      Index *pIx = pLevel->plan.u.pIdx;
      KeyInfo *pKey = sqlite3IndexKeyinfo(pParse, pIx);
      int iIdxCur = pLevel->iIdxCur;
      assert( pIx->pSchema==pTab->pSchema );
      assert( iIdxCur>=0 );
      sqlite3VdbeAddOp2(v, OP_SetNumColumns, 0, pIx->nColumn+1);
      sqlite3VdbeAddOp4(v, OP_OpenRead, iIdxCur, pIx->tnum, iDb,
                        (char*)pKey, P4_KEYINFO_HANDOFF);
      VdbeComment((v, "%s", pIx->zName));
    }
    sqlite3CodeVerifySchema(pParse, iDb);
  }
................................................................................
  pWInfo->iTop = sqlite3VdbeCurrentAddr(v);

  /* Generate the code to do the search.  Each iteration of the for
  ** loop below generates code for a single nested loop of the VM
  ** program.
  */
  notReady = ~(Bitmask)0;
  for(i=0; i<pTabList->nSrc; i++){
    notReady = codeOneLoopStart(pWInfo, i, wctrlFlags, notReady);






  }






















































































































































































































































































































































































































































  pWInfo->iContinue = pWInfo->a[i-1].addrCont;

#ifdef SQLITE_TEST  /* For testing and debugging use only */
  /* Record in the query plan information about the current table
  ** and the index used to access it (if any).  If the table itself
  ** is not used, its name is just '{}'.  If no index is used
  ** the index is listed as "{}".  If the primary key is used the
  ** index name is '*'.
................................................................................
    int n;
    pLevel = &pWInfo->a[i];
    pTabItem = &pTabList->a[pLevel->iFrom];
    z = pTabItem->zAlias;
    if( z==0 ) z = pTabItem->pTab->zName;
    n = sqlite3Strlen30(z);
    if( n+nQPlan < sizeof(sqlite3_query_plan)-10 ){
      if( pLevel->plan.wsFlags & WHERE_IDX_ONLY ){
        memcpy(&sqlite3_query_plan[nQPlan], "{}", 2);
        nQPlan += 2;
      }else{
        memcpy(&sqlite3_query_plan[nQPlan], z, n);
        nQPlan += n;
      }
      sqlite3_query_plan[nQPlan++] = ' ';
    }
    testcase( pLevel->plan.wsFlags & WHERE_ROWID_EQ );
    testcase( pLevel->plan.wsFlags & WHERE_ROWID_RANGE );
    if( pLevel->plan.wsFlags & (WHERE_ROWID_EQ|WHERE_ROWID_RANGE) ){
      memcpy(&sqlite3_query_plan[nQPlan], "* ", 2);
      nQPlan += 2;
    }else if( (pLevel->plan.wsFlags & WHERE_INDEXED)!=0 ){



      n = sqlite3Strlen30(pLevel->plan.u.pIdx->zName);
      if( n+nQPlan < sizeof(sqlite3_query_plan)-2 ){
        memcpy(&sqlite3_query_plan[nQPlan], pLevel->plan.u.pIdx->zName, n);
        nQPlan += n;
        sqlite3_query_plan[nQPlan++] = ' ';
      }
    }else{
      memcpy(&sqlite3_query_plan[nQPlan], "{} ", 3);
      nQPlan += 3;
    }
  }
  while( nQPlan>0 && sqlite3_query_plan[nQPlan-1]==' ' ){
    sqlite3_query_plan[--nQPlan] = 0;
  }
  sqlite3_query_plan[nQPlan] = 0;
  nQPlan = 0;
#endif /* SQLITE_TEST // Testing and debugging use only */

  /* Record the continuation address in the WhereInfo structure.  Then
  ** clean up and return.
  */


  return pWInfo;

  /* Jump here if malloc fails */
whereBeginError:

  whereInfoFree(db, pWInfo);
  return 0;
}

/*
** Generate the end of the WHERE loop.  See comments on 
** sqlite3WhereBegin() for additional information.
................................................................................
  for(i=pTabList->nSrc-1; i>=0; i--){
    pLevel = &pWInfo->a[i];
    sqlite3VdbeResolveLabel(v, pLevel->addrCont);
    if( pLevel->op!=OP_Noop ){
      sqlite3VdbeAddOp2(v, pLevel->op, pLevel->p1, pLevel->p2);
      sqlite3VdbeChangeP5(v, pLevel->p5);
    }
    if( pLevel->plan.wsFlags & WHERE_IN_ABLE && pLevel->u.in.nIn>0 ){
      struct InLoop *pIn;
      int j;
      sqlite3VdbeResolveLabel(v, pLevel->addrNxt);
      for(j=pLevel->u.in.nIn, pIn=&pLevel->u.in.aInLoop[j-1]; j>0; j--, pIn--){
        sqlite3VdbeJumpHere(v, pIn->addrInTop+1);
        sqlite3VdbeAddOp2(v, OP_Next, pIn->iCur, pIn->addrInTop);
        sqlite3VdbeJumpHere(v, pIn->addrInTop-1);
      }
      sqlite3DbFree(db, pLevel->u.in.aInLoop);
    }
    sqlite3VdbeResolveLabel(v, pLevel->addrBrk);
    if( pLevel->iLeftJoin ){
      int addr;
      addr = sqlite3VdbeAddOp1(v, OP_IfPos, pLevel->iLeftJoin);
      sqlite3VdbeAddOp1(v, OP_NullRow, pTabList->a[i].iCursor);
      if( pLevel->iIdxCur>=0 ){
................................................................................
  /* Close all of the cursors that were opened by sqlite3WhereBegin.
  */
  for(i=0, pLevel=pWInfo->a; i<pTabList->nSrc; i++, pLevel++){
    struct SrcList_item *pTabItem = &pTabList->a[pLevel->iFrom];
    Table *pTab = pTabItem->pTab;
    assert( pTab!=0 );
    if( (pTab->tabFlags & TF_Ephemeral)!=0 || pTab->pSelect ) continue;
    if( !pWInfo->okOnePass && (pLevel->plan.wsFlags & WHERE_IDX_ONLY)==0 ){
      sqlite3VdbeAddOp1(v, OP_Close, pTabItem->iCursor);
    }
    if( (pLevel->plan.wsFlags & WHERE_INDEXED)!=0 ){
      sqlite3VdbeAddOp1(v, OP_Close, pLevel->iIdxCur);
    }

    /* If this scan uses an index, make code substitutions to read data
    ** from the index in preference to the table. Sometimes, this means
    ** the table need never be read from. This is a performance boost,
    ** as the vdbe level waits until the table is read before actually
................................................................................
    ** 
    ** Calls to the code generator in between sqlite3WhereBegin and
    ** sqlite3WhereEnd will have created code that references the table
    ** directly.  This loop scans all that code looking for opcodes
    ** that reference the table and converts them into opcodes that
    ** reference the index.
    */
    if( (pLevel->plan.wsFlags & WHERE_INDEXED)!=0 ){
      int k, j, last;
      VdbeOp *pOp;
      Index *pIdx = pLevel->plan.u.pIdx;
      int useIndexOnly = pLevel->plan.wsFlags & WHERE_IDX_ONLY;

      assert( pIdx!=0 );
      pOp = sqlite3VdbeGetOp(v, pWInfo->iTop);
      last = sqlite3VdbeCurrentAddr(v);
      for(k=pWInfo->iTop; k<last; k++, pOp++){
        if( pOp->p1!=pLevel->iTabCur ) continue;
        if( pOp->opcode==OP_Column ){