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For FROM-clause subqueries that cannot be flattened, try to push WHERE clause

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terms of the outer query down into the subquery in order to help the subquery
run faster and/or use less memory.

FossilOrigin-Name: 297fae7551a2af9e600d833801ff79fca0602ad5
This commit is contained in:
drh
2015-06-01 20:28:03 +00:00
parent fcb9f4f3ca
commit 69b72d5a29
3 changed files with 140 additions and 58 deletions
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181
src/select.c
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@@ -3718,6 +3718,73 @@ static int flattenSubquery(
}
#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:
@@ -4816,60 +4883,72 @@ int sqlite3Select(
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));
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);
}
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 ){
if( db->mallocFailed ){
goto select_end;
}
pParse->nHeight -= sqlite3SelectExprHeight(p);