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Comment:In a query that uses a partial index, the expression that is the WHERE clause of the partial index must always be true. Use this fact to avoid evaluating identical terms in the WHERE clause of the query.
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SHA3-256: 9b2879629c34fc0a8e99d94648903eb93aabbc7a3682c80cb7382f9a9ca5ffb7
User & Date: drh 2019-03-01 18:07:05
Context
2019-03-01
21:12
Fix a minor comment typo. No code changes. check-in: 9a0a93c89d user: drh tags: trunk
18:27
Merge the latest enhancements from trunk. check-in: e64ded7b04 user: drh tags: apple-osx
18:07
In a query that uses a partial index, the expression that is the WHERE clause of the partial index must always be true. Use this fact to avoid evaluating identical terms in the WHERE clause of the query. check-in: 9b2879629c user: drh tags: trunk
2019-02-28
20:10
Add the ".parameter" command to the CLI. check-in: 1f9fa58541 user: drh tags: trunk
Changes
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Changes to src/wherecode.c.

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    x.iIdxCol = iIdxCol;
    x.pIdxExpr = aColExpr->a[iIdxCol].pExpr;
    sqlite3WalkExpr(&w, pWInfo->pWhere);
    sqlite3WalkExprList(&w, pWInfo->pOrderBy);
    sqlite3WalkExprList(&w, pWInfo->pResultSet);
  }
}





























/*
** Generate code for the start of the iLevel-th loop in the WHERE clause
** implementation described by pWInfo.
*/
Bitmask sqlite3WhereCodeOneLoopStart(
  Parse *pParse,       /* Parsing context */
................................................................................
    ** OR clause, since the transformation will become invalid once we
    ** move forward to the next index.
    ** https://sqlite.org/src/info/4e8e4857d32d401f
    */
    if( pLevel->iLeftJoin==0 && (pWInfo->wctrlFlags & WHERE_OR_SUBCLAUSE)==0 ){
      whereIndexExprTrans(pIdx, iCur, iIdxCur, pWInfo);
    }









    /* Record the instruction used to terminate the loop. */
    if( pLoop->wsFlags & WHERE_ONEROW ){
      pLevel->op = OP_Noop;
    }else if( bRev ){
      pLevel->op = OP_Prev;
    }else{







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    x.iIdxCol = iIdxCol;
    x.pIdxExpr = aColExpr->a[iIdxCol].pExpr;
    sqlite3WalkExpr(&w, pWInfo->pWhere);
    sqlite3WalkExprList(&w, pWInfo->pOrderBy);
    sqlite3WalkExprList(&w, pWInfo->pResultSet);
  }
}

/*
** The pTruth expression is always tree because it is the WHERE clause
** a partial index that is driving a query loop.  Look through all of the
** WHERE clause terms on the query, and if any of those terms must be
** true because pTruth is true, then mark those WHERE clause terms as
** coded.
*/
static void whereApplyPartialIndexConstraints(
  Expr *pTruth,
  int iTabCur,
  WhereClause *pWC
){
  int i;
  WhereTerm *pTerm;
  while( pTruth->op==TK_AND ){
    whereApplyPartialIndexConstraints(pTruth->pLeft, iTabCur, pWC);
    pTruth = pTruth->pRight;
  }
  for(i=0, pTerm=pWC->a; i<pWC->nTerm; i++, pTerm++){
    Expr *pExpr;
    if( pTerm->wtFlags & TERM_CODED ) continue;
    pExpr = pTerm->pExpr;
    if( sqlite3ExprCompare(0, pExpr, pTruth, iTabCur)==0 ){
      pTerm->wtFlags |= TERM_CODED;
    }
  }
}

/*
** Generate code for the start of the iLevel-th loop in the WHERE clause
** implementation described by pWInfo.
*/
Bitmask sqlite3WhereCodeOneLoopStart(
  Parse *pParse,       /* Parsing context */
................................................................................
    ** OR clause, since the transformation will become invalid once we
    ** move forward to the next index.
    ** https://sqlite.org/src/info/4e8e4857d32d401f
    */
    if( pLevel->iLeftJoin==0 && (pWInfo->wctrlFlags & WHERE_OR_SUBCLAUSE)==0 ){
      whereIndexExprTrans(pIdx, iCur, iIdxCur, pWInfo);
    }

    /* If a partial index is driving the loop, try to eliminate WHERE clause
    ** terms from the query that must be true due to the WHERE clause of
    ** the partial index
    */
    if( pIdx->pPartIdxWhere ){
      whereApplyPartialIndexConstraints(pIdx->pPartIdxWhere, iCur, pWC);
    }

    /* Record the instruction used to terminate the loop. */
    if( pLoop->wsFlags & WHERE_ONEROW ){
      pLevel->op = OP_Noop;
    }else if( bRev ){
      pLevel->op = OP_Prev;
    }else{