SQLite

#define WHERE_BTM_LIMIT    0x00200000  /* x>EXPR or x>=EXPR constraint */
#define WHERE_BOTH_LIMIT   0x00300000  /* Both x>EXPR and x<EXPR */
#define WHERE_IDX_ONLY     0x00400000  /* Use index only - omit table */
#define WHERE_ORDERED      0x00800000  /* Output will appear in correct order */
#define WHERE_REVERSE      0x01000000  /* Scan in reverse order */
#define WHERE_UNIQUE       0x02000000  /* Selects no more than one row */
#define WHERE_ALL_UNIQUE   0x04000000  /* This and all prior have one row */
#define WHERE_OB_UNIQUE    0x00004000  /* Values in ORDER BY columns are 
                                       ** different for every output row */
#define WHERE_VIRTUALTABLE 0x08000000  /* Use virtual-table processing */
#define WHERE_MULTI_OR     0x10000000  /* OR using multiple indices */
#define WHERE_TEMP_INDEX   0x20000000  /* Uses an ephemeral index */
#define WHERE_DISTINCT     0x40000000  /* Correct order for DISTINCT */
#define WHERE_COVER_SCAN   0x80000000  /* Full scan of a covering index */

/*

** The *pbRev value is set to 0 order 1 depending on whether or not
** pIdx should be run in the forward order or in reverse order.
*/
static int isSortingIndex(
  WhereBestIdx *p,    /* Best index search context */
  Index *pIdx,        /* The index we are testing */
  int base,           /* Cursor number for the table to be sorted */
  int *pbRev,         /* Set to 1 for reverse-order scan of pIdx */
  int *pbObUnique     /* ORDER BY column values will different in every row */
){
  int i;                        /* Number of pIdx terms used */
  int j;                        /* Number of ORDER BY terms satisfied */
  int sortOrder = 2;            /* 0: forward.  1: backward.  2: unknown */
  int nTerm;                    /* Number of ORDER BY terms */
  struct ExprList_item *pOBItem;/* A term of the ORDER BY clause */
  Table *pTab = pIdx->pTable;   /* Table that owns index pIdx */
  ExprList *pOrderBy;           /* The ORDER BY clause */
  Parse *pParse = p->pParse;    /* Parser context */
  sqlite3 *db = pParse->db;     /* Database connection */
  int nPriorSat;                /* ORDER BY terms satisfied by outer loops */
  int seenRowid = 0;            /* True if an ORDER BY rowid term is seen */
  int uniqueNotNull;            /* pIdx is UNIQUE with all terms are NOT NULL */
  int outerObUnique;            /* Outer loops generate different values in
                                ** every row for the ORDER BY columns */

  if( p->i==0 ){
    nPriorSat = 0;
    outerObUnique = 1;
  }else{
    u32 wsFlags = p->aLevel[p->i-1].plan.wsFlags;
    nPriorSat = p->aLevel[p->i-1].plan.nOBSat;
    if( (wsFlags & WHERE_ORDERED)==0 ){
      /* This loop cannot be ordered unless the next outer loop is
      ** also ordered */
      return nPriorSat;
    }
    if( OptimizationDisabled(db, SQLITE_OrderByIdxJoin) ){
      /* Only look at the outer-most loop if the OrderByIdxJoin
      ** optimization is disabled */
      return nPriorSat;
    }
    testcase( wsFlags & WHERE_OB_UNIQUE );
    testcase( wsFlags & WHERE_ALL_UNIQUE );
    outerObUnique = (wsFlags & (WHERE_OB_UNIQUE|WHERE_ALL_UNIQUE))!=0;
  }
  pOrderBy = p->pOrderBy;
  assert( pOrderBy!=0 );
  if( pIdx->bUnordered ){
    /* Hash indices (indicated by the "unordered" tag on sqlite_stat1) cannot
    ** be used for sorting */
    return nPriorSat;

    }else if( pTab->aCol[iColumn].notNull==0 && isEq!=1 ){
      testcase( isEq==0 );
      testcase( isEq==2 );
      testcase( isEq==3 );
      uniqueNotNull = 0;
    }
  }
  if( seenRowid ){
    uniqueNotNull = 1;
  }else if( uniqueNotNull==0 || i<pIdx->nColumn ){
    uniqueNotNull = 0;
  }

  /* If we have not found at least one ORDER BY term that matches the
  ** index, then show no progress. */
  if( pOBItem==&pOrderBy->a[nPriorSat] ) return nPriorSat;

  /* Either the outer queries must generate rows where there are no two
  ** rows with the same values in all ORDER BY columns, or else this
  ** loop must generate just a single row of output.  Example:  Suppose
  ** the outer loops generate A=1 and A=1, and this loop generates B=3
  ** and B=4.  Then without the following test, ORDER BY A,B would 
  ** generate the wrong order output: 1,3 1,4 1,3 1,4
  */
  if( outerObUnique==0 && uniqueNotNull==0 ) return nPriorSat;
  *pbObUnique = uniqueNotNull;

  /* Return the necessary scan order back to the caller */
  *pbRev = sortOrder & 1;

  /* If there was an "ORDER BY rowid" term that matched, or it is only
  ** possible for a single row from this table to match, then skip over
  ** any additional ORDER BY terms dealing with this table.
  */
  if( uniqueNotNull ){
    /* Advance j over additional ORDER BY terms associated with base */
    WhereMaskSet *pMS = p->pWC->pMaskSet;
    Bitmask m = ~getMask(pMS, base);
    while( j<nTerm && (exprTableUsage(pMS, pOrderBy->a[j].pExpr)&m)==0 ){
      j++;
    }
  }

    /* If there is an ORDER BY clause and the index being considered will
    ** naturally scan rows in the required order, set the appropriate flags
    ** in pc.plan.wsFlags. Otherwise, if there is an ORDER BY clause but
    ** the index will scan rows in a different order, set the bSort
    ** variable.  */
    if( bSort && (pSrc->jointype & JT_LEFT)==0 ){
      int bRev = 2;
      int bObUnique = 0;
      WHERETRACE(("      --> before isSortIndex: nPriorSat=%d\n",nPriorSat));
      pc.plan.nOBSat = isSortingIndex(p, pProbe, iCur, &bRev, &bObUnique);
      WHERETRACE(("      --> after  isSortIndex: bRev=%d bObU=%d nOBSat=%d\n",
                  bRev, bObUnique, pc.plan.nOBSat));
      if( nPriorSat<pc.plan.nOBSat || (pc.plan.wsFlags & WHERE_ALL_UNIQUE)!=0 ){
        pc.plan.wsFlags |= WHERE_ORDERED;
        if( bObUnique ) pc.plan.wsFlags |= WHERE_OB_UNIQUE;
      }
      if( nOrderBy==pc.plan.nOBSat ){
        bSort = 0;
        pc.plan.wsFlags |= WHERE_ROWID_RANGE|WHERE_COLUMN_RANGE;
      }
      if( bRev & 1 ) pc.plan.wsFlags |= WHERE_REVERSE;
    }

    ** on one page and hence more pages have to be fetched.
    **
    ** The ANALYZE command and the sqlite_stat1 and sqlite_stat3 tables do
    ** not give us data on the relative sizes of table and index records.
    ** So this computation assumes table records are about twice as big
    ** as index records
    */
    if( (pc.plan.wsFlags&~(WHERE_REVERSE|WHERE_ORDERED|WHERE_OB_UNIQUE))
                                                              ==WHERE_IDX_ONLY
     && (pWC->wctrlFlags & WHERE_ONEPASS_DESIRED)==0
     && sqlite3GlobalConfig.bUseCis
     && OptimizationEnabled(pParse->db, SQLITE_CoverIdxScan)
    ){
      /* This index is not useful for indexing, but it is a covering index.
      ** A full-scan of the index might be a little faster than a full-scan
      ** of the table, so give this case a cost slightly less than a table

# 2013 March 26
#
# The author disclaims copyright to this source code.  In place of
# a legal notice, here is a blessing:
#
#    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.
#
#***********************************************************************
# This file implements regression tests for SQLite library.  The
# focus of this file is testing that the optimizations that disable
# ORDER BY clauses work correctly on multi-value primary keys and
# unique indices when only some prefix of the terms in the key are
# used.  See ticket http://www.sqlite.org/src/info/a179fe74659
#


set testdir [file dirname $argv0]
source $testdir/tester.tcl
set ::testprefix orderby4

# Generate test data for a join.  Verify that the join gets the
# correct answer.
#
do_execsql_test 1.1 {
  CREATE TABLE t1(a, b, PRIMARY KEY(a,b));
  INSERT INTO t1 VALUES(1,1),(1,2);
  CREATE TABLE t2(x, y, PRIMARY KEY(x,y));
  INSERT INTO t2 VALUES(3,3),(4,4);
  SELECT a, x FROM t1, t2 ORDER BY 1, 2;
} {1 3 1 3 1 4 1 4}
do_execsql_test 1.2 {
  SELECT a, x FROM t1 CROSS JOIN t2 ORDER BY 1, 2;
} {1 3 1 3 1 4 1 4}
do_execsql_test 1.3 {
  SELECT a, x FROM t2 CROSS JOIN t1 ORDER BY 1, 2;
} {1 3 1 3 1 4 1 4}

do_execsql_test 2.1 {
  CREATE TABLE t3(a);
  INSERT INTO t3 VALUES(1),(1);
  CREATE INDEX t3a ON t3(a);
  CREATE TABLE t4(x);
  INSERT INTO t4 VALUES(3),(4);
  CREATE INDEX t4x ON t4(x);
  SELECT a, x FROM t3, t4 ORDER BY 1, 2;
} {1 3 1 3 1 4 1 4}
do_execsql_test 2.2 {
  SELECT a, x FROM t3 CROSS JOIN t4 ORDER BY 1, 2;
} {1 3 1 3 1 4 1 4}
do_execsql_test 2.3 {
  SELECT a, x FROM t4 CROSS JOIN t3 ORDER BY 1, 2;
} {1 3 1 3 1 4 1 4}

finish_test