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Comment:For FROM-clause subqueries that cannot be flattened, try to push WHERE clause terms of the outer query down into the subquery in order to help the subquery run faster and/or use less memory.
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SHA1:297fae7551a2af9e600d833801ff79fca0602ad5
User & Date: drh 2015-06-01 20:28:03
Context
2015-06-02
18:09
For FROM-clause subqueries that cannot be flattened, try to push relevant WHERE clause terms of the outer query down into the subquery in order to help the subquery run faster and/or use less memory. check-in: 6df18e94 user: drh tags: trunk
2015-06-01
20:28
For FROM-clause subqueries that cannot be flattened, try to push WHERE clause terms of the outer query down into the subquery in order to help the subquery run faster and/or use less memory. Closed-Leaf check-in: 297fae75 user: drh tags: subquery-opt
18:13
Corrections to comments in expr.c. No code changes. check-in: f925389e user: drh tags: trunk
Changes
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Changes to src/select.c.

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  }
#endif

  return 1;
}
#endif /* !defined(SQLITE_OMIT_SUBQUERY) || !defined(SQLITE_OMIT_VIEW) */




































































/*
** Based on the contents of the AggInfo structure indicated by the first
** argument, this function checks if the following are true:
**
**    * the query contains just a single aggregate function,
**    * the aggregate function is either min() or max(), and
**    * the argument to the aggregate function is a column value.
................................................................................
    if( flattenSubquery(pParse, p, i, isAgg, isAggSub) ){
      /* This subquery can be absorbed into its parent. */
      if( isAggSub ){
        isAgg = 1;
        p->selFlags |= SF_Aggregate;
      }
      i = -1;











    }else if( pTabList->nSrc==1
           && (p->selFlags & SF_All)==0
           && OptimizationEnabled(db, SQLITE_SubqCoroutine)
    ){
      /* Implement a co-routine that will return a single row of the result
      ** set on each invocation.
      */
      int addrTop = sqlite3VdbeCurrentAddr(v)+1;
      pItem->regReturn = ++pParse->nMem;
      sqlite3VdbeAddOp3(v, OP_InitCoroutine, pItem->regReturn, 0, addrTop);
      VdbeComment((v, "%s", pItem->pTab->zName));
      pItem->addrFillSub = addrTop;
      sqlite3SelectDestInit(&dest, SRT_Coroutine, pItem->regReturn);
      explainSetInteger(pItem->iSelectId, (u8)pParse->iNextSelectId);
      sqlite3Select(pParse, pSub, &dest);
      pItem->pTab->nRowLogEst = sqlite3LogEst(pSub->nSelectRow);
      pItem->viaCoroutine = 1;
      pItem->regResult = dest.iSdst;
      sqlite3VdbeAddOp1(v, OP_EndCoroutine, pItem->regReturn);
      sqlite3VdbeJumpHere(v, addrTop-1);
      sqlite3ClearTempRegCache(pParse);
    }else{
      /* Generate a subroutine that will fill an ephemeral table with
      ** the content of this subquery.  pItem->addrFillSub will point
      ** to the address of the generated subroutine.  pItem->regReturn
      ** is a register allocated to hold the subroutine return address
      */
      int topAddr;
      int onceAddr = 0;
      int retAddr;
      assert( pItem->addrFillSub==0 );
      pItem->regReturn = ++pParse->nMem;
      topAddr = sqlite3VdbeAddOp2(v, OP_Integer, 0, pItem->regReturn);
      pItem->addrFillSub = topAddr+1;
      if( pItem->isCorrelated==0 ){
        /* If the subquery is not correlated and if we are not inside of
        ** a trigger, then we only need to compute the value of the subquery
        ** once. */
        onceAddr = sqlite3CodeOnce(pParse); VdbeCoverage(v);
        VdbeComment((v, "materialize \"%s\"", pItem->pTab->zName));
      }else{
        VdbeNoopComment((v, "materialize \"%s\"", pItem->pTab->zName));
      }
      sqlite3SelectDestInit(&dest, SRT_EphemTab, pItem->iCursor);
      explainSetInteger(pItem->iSelectId, (u8)pParse->iNextSelectId);
      sqlite3Select(pParse, pSub, &dest);
      pItem->pTab->nRowLogEst = sqlite3LogEst(pSub->nSelectRow);
      if( onceAddr ) sqlite3VdbeJumpHere(v, onceAddr);
      retAddr = sqlite3VdbeAddOp1(v, OP_Return, pItem->regReturn);
      VdbeComment((v, "end %s", pItem->pTab->zName));
      sqlite3VdbeChangeP1(v, topAddr, retAddr);
      sqlite3ClearTempRegCache(pParse);
    }

    if( /*pParse->nErr ||*/ db->mallocFailed ){
      goto select_end;
    }
    pParse->nHeight -= sqlite3SelectExprHeight(p);
    pTabList = p->pSrc;
    if( !IgnorableOrderby(pDest) ){
      sSort.pOrderBy = p->pOrderBy;
    }







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  }
#endif

  return 1;
}
#endif /* !defined(SQLITE_OMIT_SUBQUERY) || !defined(SQLITE_OMIT_VIEW) */



#if !defined(SQLITE_OMIT_SUBQUERY) || !defined(SQLITE_OMIT_VIEW)
/*
** Make copies of relevant WHERE clause terms of the outer query into
** the WHERE clause of subquery.  Example:
**
**    SELECT * FROM (SELECT a AS x, c-d AS y FROM t1) WHERE x=5 AND y=10;
**
** Transformed into:
**
**    SELECT * FROM (SELECT a AS x, c-d AS y FROM t1 WHERE a=5 AND c-d=10)
**     WHERE x=5 AND y=10;
**
** The hope is that the terms added to the inner query will make it more
** efficient.
**
** Do not attempt this optimization if:
**
**   (1) The inner query is an aggregate.  (In that case, we'd really want
**       to copy the outer WHERE-clause terms onto the HAVING clause of the
**       inner query.  But they probably won't help there so do not bother.)
**
**   (2) The inner query is the recursive part of a common table expression.
**
**   (3) The inner query has a LIMIT clause (since the changes to the WHERE
**       close would change the meaning of the LIMIT).
**
**   (4) The inner query is the right operand of a LEFT JOIN.  (The caller
**       enforces this restriction since this routine does not have enough
**       information to know.)
**
** Return 0 if no changes are made and non-zero if one or more WHERE clause
** terms are duplicated into the subquery.
*/
static int pushDownWhereTerms(
  sqlite3 *db,          /* The database connection (for malloc()) */
  Select *pSubq,        /* The subquery whose WHERE clause is to be augmented */
  Expr *pWhere,         /* The WHERE clause of the outer query */
  int iCursor           /* Cursor number of the subquery */
){
  Expr *pNew;
  int nChng = 0;
  if( pWhere==0 ) return 0;
  if( (pSubq->selFlags & (SF_Aggregate|SF_Recursive))!=0 ){
     return 0; /* restrictions (1) and (2) */
  }
  if( pSubq->pLimit!=0 ){
     return 0; /* restriction (3) */
  }
  while( pWhere->op==TK_AND ){
    nChng += pushDownWhereTerms(db, pSubq, pWhere->pRight, iCursor);
    pWhere = pWhere->pLeft;
  }
  if( sqlite3ExprIsTableConstant(pWhere, iCursor) ){
    nChng++;
    while( pSubq ){
      pNew = sqlite3ExprDup(db, pWhere, 0);
      pNew = substExpr(db, pNew, iCursor, pSubq->pEList);
      pSubq->pWhere = sqlite3ExprAnd(db, pSubq->pWhere, pNew);
      pSubq = pSubq->pPrior;
    }
  }
  return nChng;
}
#endif /* !defined(SQLITE_OMIT_SUBQUERY) || !defined(SQLITE_OMIT_VIEW) */

/*
** Based on the contents of the AggInfo structure indicated by the first
** argument, this function checks if the following are true:
**
**    * the query contains just a single aggregate function,
**    * the aggregate function is either min() or max(), and
**    * the argument to the aggregate function is a column value.
................................................................................
    if( flattenSubquery(pParse, p, i, isAgg, isAggSub) ){
      /* This subquery can be absorbed into its parent. */
      if( isAggSub ){
        isAgg = 1;
        p->selFlags |= SF_Aggregate;
      }
      i = -1;
    }else{
      if( (pItem->jointype & JT_OUTER)==0
       && pushDownWhereTerms(db, pSub, p->pWhere, pItem->iCursor)
      ){
#if SELECTTRACE_ENABLED
        if( sqlite3SelectTrace & 0x100 ){
          sqlite3DebugPrintf("After WHERE-clause push-down:\n");
          sqlite3TreeViewSelect(0, p, 0);
        }
#endif
      }
      if( pTabList->nSrc==1
       && (p->selFlags & SF_All)==0
       && OptimizationEnabled(db, SQLITE_SubqCoroutine)
      ){
        /* Implement a co-routine that will return a single row of the result
        ** set on each invocation.
        */
        int addrTop = sqlite3VdbeCurrentAddr(v)+1;
        pItem->regReturn = ++pParse->nMem;
        sqlite3VdbeAddOp3(v, OP_InitCoroutine, pItem->regReturn, 0, addrTop);
        VdbeComment((v, "%s", pItem->pTab->zName));
        pItem->addrFillSub = addrTop;
        sqlite3SelectDestInit(&dest, SRT_Coroutine, pItem->regReturn);
        explainSetInteger(pItem->iSelectId, (u8)pParse->iNextSelectId);
        sqlite3Select(pParse, pSub, &dest);
        pItem->pTab->nRowLogEst = sqlite3LogEst(pSub->nSelectRow);
        pItem->viaCoroutine = 1;
        pItem->regResult = dest.iSdst;
        sqlite3VdbeAddOp1(v, OP_EndCoroutine, pItem->regReturn);
        sqlite3VdbeJumpHere(v, addrTop-1);
        sqlite3ClearTempRegCache(pParse);
      }else{
        /* Generate a subroutine that will fill an ephemeral table with
        ** the content of this subquery.  pItem->addrFillSub will point
        ** to the address of the generated subroutine.  pItem->regReturn
        ** is a register allocated to hold the subroutine return address
        */
        int topAddr;
        int onceAddr = 0;
        int retAddr;
        assert( pItem->addrFillSub==0 );
        pItem->regReturn = ++pParse->nMem;
        topAddr = sqlite3VdbeAddOp2(v, OP_Integer, 0, pItem->regReturn);
        pItem->addrFillSub = topAddr+1;
        if( pItem->isCorrelated==0 ){
          /* If the subquery is not correlated and if we are not inside of
          ** a trigger, then we only need to compute the value of the subquery
          ** once. */
          onceAddr = sqlite3CodeOnce(pParse); VdbeCoverage(v);
          VdbeComment((v, "materialize \"%s\"", pItem->pTab->zName));
        }else{
          VdbeNoopComment((v, "materialize \"%s\"", pItem->pTab->zName));
        }
        sqlite3SelectDestInit(&dest, SRT_EphemTab, pItem->iCursor);
        explainSetInteger(pItem->iSelectId, (u8)pParse->iNextSelectId);
        sqlite3Select(pParse, pSub, &dest);
        pItem->pTab->nRowLogEst = sqlite3LogEst(pSub->nSelectRow);
        if( onceAddr ) sqlite3VdbeJumpHere(v, onceAddr);
        retAddr = sqlite3VdbeAddOp1(v, OP_Return, pItem->regReturn);
        VdbeComment((v, "end %s", pItem->pTab->zName));
        sqlite3VdbeChangeP1(v, topAddr, retAddr);
        sqlite3ClearTempRegCache(pParse);
      }
    }
    if( db->mallocFailed ){
      goto select_end;
    }
    pParse->nHeight -= sqlite3SelectExprHeight(p);
    pTabList = p->pSrc;
    if( !IgnorableOrderby(pDest) ){
      sSort.pOrderBy = p->pOrderBy;
    }