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Overview
Comment:When testing non-indexed WHERE constraints, test those that involve correlated sub-queries last of all. This increases the chances of not having to run the sub-query at all.
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SHA3-256: 1f9c1f359e4693954ba7e2bc7b172ef34eb046e4ca2796df8336975b9d6aa92b
User & Date: dan 2017-07-10 14:33:00
Context
2017-07-10
14:39
Fix a problem causing non-covered WHERE terms to be evaluated before covered WHERE terms. check-in: 7d3cb39f user: dan tags: defer-where-subqueries
14:33
When testing non-indexed WHERE constraints, test those that involve correlated sub-queries last of all. This increases the chances of not having to run the sub-query at all. check-in: 1f9c1f35 user: dan tags: defer-where-subqueries
13:24
For sqlite3TreeView() debugging output, show the Expr.flags field on scalar subqueries. check-in: dc857a96 user: drh tags: trunk
Changes
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Changes to src/sqliteInt.h.

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#define EP_Subquery  0x200000 /* Tree contains a TK_SELECT operator */
#define EP_Alias     0x400000 /* Is an alias for a result set column */
#define EP_Leaf      0x800000 /* Expr.pLeft, .pRight, .u.pSelect all NULL */

/*
** Combinations of two or more EP_* flags
*/
#define EP_Propagate (EP_Collate|EP_Subquery) /* Propagate these bits up tree */

/*
** These macros can be used to test, set, or clear bits in the
** Expr.flags field.
*/
#define ExprHasProperty(E,P)     (((E)->flags&(P))!=0)
#define ExprHasAllProperty(E,P)  (((E)->flags&(P))==(P))







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#define EP_Subquery  0x200000 /* Tree contains a TK_SELECT operator */
#define EP_Alias     0x400000 /* Is an alias for a result set column */
#define EP_Leaf      0x800000 /* Expr.pLeft, .pRight, .u.pSelect all NULL */

/*
** Combinations of two or more EP_* flags
*/
#define EP_Propagate (EP_Collate|EP_Subquery|EP_VarSelect) /* Prop. up tree */

/*
** These macros can be used to test, set, or clear bits in the
** Expr.flags field.
*/
#define ExprHasProperty(E,P)     (((E)->flags&(P))!=0)
#define ExprHasAllProperty(E,P)  (((E)->flags&(P))==(P))

Changes to src/wherecode.c.

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  struct SrcList_item *pTabItem;  /* FROM clause term being coded */
  int addrBrk;                    /* Jump here to break out of the loop */
  int addrHalt;                   /* addrBrk for the outermost loop */
  int addrCont;                   /* Jump here to continue with next cycle */
  int iRowidReg = 0;        /* Rowid is stored in this register, if not zero */
  int iReleaseReg = 0;      /* Temp register to free before returning */
  Index *pIdx = 0;          /* Index used by loop (if any) */
  int loopAgain;            /* True if constraint generator loop should repeat */

  pParse = pWInfo->pParse;
  v = pParse->pVdbe;
  pWC = &pWInfo->sWC;
  db = pParse->db;
  pLevel = &pWInfo->a[iLevel];
  pLoop = pLevel->pWLoop;
................................................................................
#ifdef SQLITE_ENABLE_STMT_SCANSTATUS
  pLevel->addrVisit = sqlite3VdbeCurrentAddr(v);
#endif

  /* Insert code to test every subexpression that can be completely
  ** computed using the current set of tables.
  **
  ** This loop may run either once (pIdx==0) or twice (pIdx!=0). If
  ** it is run twice, then the first iteration codes those sub-expressions
  ** that can be computed using columns from pIdx only (without seeking
  ** the main table cursor). 






  */

  do{
    loopAgain = 0;

    for(pTerm=pWC->a, j=pWC->nTerm; j>0; j--, pTerm++){
      Expr *pE;
      int skipLikeAddr = 0;
      testcase( pTerm->wtFlags & TERM_VIRTUAL );
      testcase( pTerm->wtFlags & TERM_CODED );
      if( pTerm->wtFlags & (TERM_VIRTUAL|TERM_CODED) ) continue;
      if( (pTerm->prereqAll & pLevel->notReady)!=0 ){
................................................................................
        continue;
      }
      pE = pTerm->pExpr;
      assert( pE!=0 );
      if( pLevel->iLeftJoin && !ExprHasProperty(pE, EP_FromJoin) ){
        continue;
      }

      if( pIdx && !sqlite3ExprCoveredByIndex(pE, pLevel->iTabCur, pIdx) ){
        loopAgain = 1;

        continue;
      }





      if( pTerm->wtFlags & TERM_LIKECOND ){
        /* If the TERM_LIKECOND flag is set, that means that the range search
        ** is sufficient to guarantee that the LIKE operator is true, so we
        ** can skip the call to the like(A,B) function.  But this only works
        ** for strings.  So do not skip the call to the function on the pass
        ** that compares BLOBs. */
#ifdef SQLITE_LIKE_DOESNT_MATCH_BLOBS
................................................................................
        VdbeCoverage(v);
#endif
      }
      sqlite3ExprIfFalse(pParse, pE, addrCont, SQLITE_JUMPIFNULL);
      if( skipLikeAddr ) sqlite3VdbeJumpHere(v, skipLikeAddr);
      pTerm->wtFlags |= TERM_CODED;
    }
    pIdx = 0;
  }while( loopAgain );

  /* Insert code to test for implied constraints based on transitivity
  ** of the "==" operator.
  **
  ** Example: If the WHERE clause contains "t1.a=t2.b" and "t2.b=123"
  ** and we are coding the t1 loop and the t2 loop has not yet coded,
  ** then we cannot use the "t1.a=t2.b" constraint, but we can code







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  struct SrcList_item *pTabItem;  /* FROM clause term being coded */
  int addrBrk;                    /* Jump here to break out of the loop */
  int addrHalt;                   /* addrBrk for the outermost loop */
  int addrCont;                   /* Jump here to continue with next cycle */
  int iRowidReg = 0;        /* Rowid is stored in this register, if not zero */
  int iReleaseReg = 0;      /* Temp register to free before returning */
  Index *pIdx = 0;          /* Index used by loop (if any) */
  int iLoop;                /* Iteration of constraint generator loop */

  pParse = pWInfo->pParse;
  v = pParse->pVdbe;
  pWC = &pWInfo->sWC;
  db = pParse->db;
  pLevel = &pWInfo->a[iLevel];
  pLoop = pLevel->pWLoop;
................................................................................
#ifdef SQLITE_ENABLE_STMT_SCANSTATUS
  pLevel->addrVisit = sqlite3VdbeCurrentAddr(v);
#endif

  /* Insert code to test every subexpression that can be completely
  ** computed using the current set of tables.
  **
  ** This loop may run between one and three times, depending on the
  ** constraints to be generated. The value of stack variable iLoop
  ** determines the constraints coded by each iteration, as follows:
  **
  ** iLoop==1: Code only expressions that are entirely covered by pIdx.
  ** iLoop==2: Code remaining expressions that do not contain correlated
  **           sub-queries.  
  ** iLoop==3: Code all remaining expressions.
  **
  ** An effort is made to skip unnecessary iterations of the loop.
  */
  iLoop = (pIdx ? 1 : 2);
  do{

    int iNext = 0;                /* Next value for iLoop */
    for(pTerm=pWC->a, j=pWC->nTerm; j>0; j--, pTerm++){
      Expr *pE;
      int skipLikeAddr = 0;
      testcase( pTerm->wtFlags & TERM_VIRTUAL );
      testcase( pTerm->wtFlags & TERM_CODED );
      if( pTerm->wtFlags & (TERM_VIRTUAL|TERM_CODED) ) continue;
      if( (pTerm->prereqAll & pLevel->notReady)!=0 ){
................................................................................
        continue;
      }
      pE = pTerm->pExpr;
      assert( pE!=0 );
      if( pLevel->iLeftJoin && !ExprHasProperty(pE, EP_FromJoin) ){
        continue;
      }
      
      if( iNext==1 && !sqlite3ExprCoveredByIndex(pE, pLevel->iTabCur, pIdx) ){

        iNext = 2;
        continue;
      }
      if( iLoop<3 && (pE->flags & EP_VarSelect) ){
        if( iNext==0 ) iNext = 3;
        continue;
      }

      if( pTerm->wtFlags & TERM_LIKECOND ){
        /* If the TERM_LIKECOND flag is set, that means that the range search
        ** is sufficient to guarantee that the LIKE operator is true, so we
        ** can skip the call to the like(A,B) function.  But this only works
        ** for strings.  So do not skip the call to the function on the pass
        ** that compares BLOBs. */
#ifdef SQLITE_LIKE_DOESNT_MATCH_BLOBS
................................................................................
        VdbeCoverage(v);
#endif
      }
      sqlite3ExprIfFalse(pParse, pE, addrCont, SQLITE_JUMPIFNULL);
      if( skipLikeAddr ) sqlite3VdbeJumpHere(v, skipLikeAddr);
      pTerm->wtFlags |= TERM_CODED;
    }
    iLoop = iNext;
  }while( iLoop>0 );

  /* Insert code to test for implied constraints based on transitivity
  ** of the "==" operator.
  **
  ** Example: If the WHERE clause contains "t1.a=t2.b" and "t2.b=123"
  ** and we are coding the t1 loop and the t2 loop has not yet coded,
  ** then we cannot use the "t1.a=t2.b" constraint, but we can code