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SQLite training in Houston TX on 2019-11-05 (details)
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Overview
Comment:Minor size and performance improvements to the push-down optimization.
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SHA3-256: 91dfb61a1a25763bb0b5c1e353a9d584bc6de3f6eb445f54202ffe7f6fee6e8d
User & Date: drh 2017-04-29 14:56:55
Context
2017-04-29
15:27
Evaluate WHERE clause terms that reference only the index before evaluating terms that require the table, and thereby avoid seeking the table row if index terms are false. This is called the "push-down" optimization in the MySQL world, we are told. check-in: d7bb79ed user: drh tags: trunk
14:56
Minor size and performance improvements to the push-down optimization. Closed-Leaf check-in: 91dfb61a user: drh tags: pushdown-optimization
2017-04-28
19:59
Within a loop that uses a non-covering index test, test non-indexed terms that can be tested without seeking the main table cursor before those that cannot. check-in: afe68f0a user: dan tags: pushdown-optimization
Changes
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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) */


  pParse = pWInfo->pParse;
  v = pParse->pVdbe;
  pWC = &pWInfo->sWC;
  db = pParse->db;
  pLevel = &pWInfo->a[iLevel];
  pLoop = pLevel->pWLoop;
................................................................................

  /* 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).  */
  while( 1 ){



    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 ){
................................................................................
        testcase( pWInfo->untestedTerms==0
            && (pWInfo->wctrlFlags & WHERE_OR_SUBCLAUSE)!=0 );
        pWInfo->untestedTerms = 1;
        continue;
      }
      pE = pTerm->pExpr;
      assert( pE!=0 );
      if( pIdx && !sqlite3ExprCoveredByIndex(pE, pLevel->iTabCur, pIdx) ){
        continue;
      }
      if( pLevel->iLeftJoin && !ExprHasProperty(pE, EP_FromJoin) ){

        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
................................................................................
        VdbeCoverage(v);
#endif
      }
      sqlite3ExprIfFalse(pParse, pE, addrCont, SQLITE_JUMPIFNULL);
      if( skipLikeAddr ) sqlite3VdbeJumpHere(v, skipLikeAddr);
      pTerm->wtFlags |= TERM_CODED;
    }
    if( pIdx==0 ) break;
    pIdx = 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







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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;
................................................................................

  /* 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 ){
................................................................................
        testcase( pWInfo->untestedTerms==0
            && (pWInfo->wctrlFlags & WHERE_OR_SUBCLAUSE)!=0 );
        pWInfo->untestedTerms = 1;
        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
................................................................................
        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