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Merge the sqlite3WhereBegin() simplification from trunk.

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FossilOrigin-Name: 41ba2dfdd3a18671fc78d60935a16fa50f36af3d6481eff2ca9fba88e7093997
This commit is contained in:
drh
2021-12-03 19:10:17 +00:00
parent 2b05905521 70b403b667
commit 7439d3580c
3 changed files with 109 additions and 76 deletions
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171
src/where.c
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@@ -4751,6 +4751,96 @@ static void showAllWhereLoops(WhereInfo *pWInfo, WhereClause *pWC){
# define WHERETRACE_ALL_LOOPS(W,C)
#endif
/* Attempt to omit tables from a join that do not affect the result.
** For a table to not affect the result, the following must be true:
**
** 1) The query must not be an aggregate.
** 2) The table must be the RHS of a LEFT JOIN.
** 3) Either the query must be DISTINCT, or else the ON or USING clause
** must contain a constraint that limits the scan of the table to
** at most a single row.
** 4) The table must not be referenced by any part of the query apart
** from its own USING or ON clause.
**
** For example, given:
**
** CREATE TABLE t1(ipk INTEGER PRIMARY KEY, v1);
** CREATE TABLE t2(ipk INTEGER PRIMARY KEY, v2);
** CREATE TABLE t3(ipk INTEGER PRIMARY KEY, v3);
**
** then table t2 can be omitted from the following:
**
** SELECT v1, v3 FROM t1
** LEFT JOIN t2 ON (t1.ipk=t2.ipk)
** LEFT JOIN t3 ON (t1.ipk=t3.ipk)
**
** or from:
**
** SELECT DISTINCT v1, v3 FROM t1
** LEFT JOIN t2
** LEFT JOIN t3 ON (t1.ipk=t3.ipk)
*/
static SQLITE_NOINLINE Bitmask whereOmitNoopJoin(
WhereInfo *pWInfo,
Bitmask notReady
){
int i;
Bitmask tabUsed;
/* Preconditions checked by the caller */
assert( pWInfo->nLevel>=2 );
assert( OptimizationEnabled(pWInfo->pParse->db, SQLITE_OmitNoopJoin) );
/* These two preconditions checked by the caller combine to guarantee
** condition (1) of the header comment */
assert( pWInfo->pResultSet!=0 );
assert( 0==(pWInfo->wctrlFlags & WHERE_AGG_DISTINCT) );
tabUsed = sqlite3WhereExprListUsage(&pWInfo->sMaskSet, pWInfo->pResultSet);
if( pWInfo->pOrderBy ){
tabUsed |= sqlite3WhereExprListUsage(&pWInfo->sMaskSet, pWInfo->pOrderBy);
}
for(i=pWInfo->nLevel-1; i>=1; i--){
WhereTerm *pTerm, *pEnd;
SrcItem *pItem;
WhereLoop *pLoop;
pLoop = pWInfo->a[i].pWLoop;
pItem = &pWInfo->pTabList->a[pLoop->iTab];
if( (pItem->fg.jointype & JT_LEFT)==0 ) continue;
if( (pWInfo->wctrlFlags & WHERE_WANT_DISTINCT)==0
&& (pLoop->wsFlags & WHERE_ONEROW)==0
){
continue;
}
if( (tabUsed & pLoop->maskSelf)!=0 ) continue;
pEnd = pWInfo->sWC.a + pWInfo->sWC.nTerm;
for(pTerm=pWInfo->sWC.a; pTerm<pEnd; pTerm++){
if( (pTerm->prereqAll & pLoop->maskSelf)!=0 ){
if( !ExprHasProperty(pTerm->pExpr, EP_FromJoin)
|| pTerm->pExpr->iRightJoinTable!=pItem->iCursor
){
break;
}
}
}
if( pTerm<pEnd ) continue;
WHERETRACE(0xffff, ("-> drop loop %c not used\n", pLoop->cId));
notReady &= ~pLoop->maskSelf;
for(pTerm=pWInfo->sWC.a; pTerm<pEnd; pTerm++){
if( (pTerm->prereqAll & pLoop->maskSelf)!=0 ){
pTerm->wtFlags |= TERM_CODED;
}
}
if( i!=pWInfo->nLevel-1 ){
int nByte = (pWInfo->nLevel-1-i) * sizeof(WhereLevel);
memmove(&pWInfo->a[i], &pWInfo->a[i+1], nByte);
}
pWInfo->nLevel--;
assert( pWInfo->nLevel>0 );
}
return notReady;
}
/*
** Generate the beginning of the loop used for WHERE clause processing.
** The return value is a pointer to an opaque structure that contains
@@ -5119,34 +5209,15 @@ WhereInfo *sqlite3WhereBegin(
}
#endif
/* Attempt to omit tables from the join that do not affect the result.
** For a table to not affect the result, the following must be true:
/* Attempt to omit tables from a join that do not affect the result.
** See the comment on whereOmitNoopJoin() for further information.
**
** 1) The query must not be an aggregate.
** 2) The table must be the RHS of a LEFT JOIN.
** 3) Either the query must be DISTINCT, or else the ON or USING clause
** must contain a constraint that limits the scan of the table to
** at most a single row.
** 4) The table must not be referenced by any part of the query apart
** from its own USING or ON clause.
**
** For example, given:
**
** CREATE TABLE t1(ipk INTEGER PRIMARY KEY, v1);
** CREATE TABLE t2(ipk INTEGER PRIMARY KEY, v2);
** CREATE TABLE t3(ipk INTEGER PRIMARY KEY, v3);
**
** then table t2 can be omitted from the following:
**
** SELECT v1, v3 FROM t1
** LEFT JOIN t2 ON (t1.ipk=t2.ipk)
** LEFT JOIN t3 ON (t1.ipk=t3.ipk)
**
** or from:
**
** SELECT DISTINCT v1, v3 FROM t1
** LEFT JOIN t2
** LEFT JOIN t3 ON (t1.ipk=t3.ipk)
** This query optimization is factored out into a separate "no-inline"
** procedure to keep the sqlite3WhereBegin() procedure from becoming
** too large. If sqlite3WhereBegin() becomes too large, that prevents
** some C-compiler optimizers from in-lining the
** sqlite3WhereCodeOneLoopStart() procedure, and it is important to
** in-line sqlite3WhereCodeOneLoopStart() for performance reasons.
*/
notReady = ~(Bitmask)0;
if( pWInfo->nLevel>=2
@@ -5154,49 +5225,11 @@ WhereInfo *sqlite3WhereBegin(
&& 0==(wctrlFlags & WHERE_AGG_DISTINCT) /* condition (1) above */
&& OptimizationEnabled(db, SQLITE_OmitNoopJoin)
){
int i;
Bitmask tabUsed = sqlite3WhereExprListUsage(pMaskSet, pResultSet);
if( sWLB.pOrderBy ){
tabUsed |= sqlite3WhereExprListUsage(pMaskSet, sWLB.pOrderBy);
}
for(i=pWInfo->nLevel-1; i>=1; i--){
WhereTerm *pTerm, *pEnd;
SrcItem *pItem;
pLoop = pWInfo->a[i].pWLoop;
pItem = &pWInfo->pTabList->a[pLoop->iTab];
if( (pItem->fg.jointype & JT_LEFT)==0 ) continue;
if( (wctrlFlags & WHERE_WANT_DISTINCT)==0
&& (pLoop->wsFlags & WHERE_ONEROW)==0
){
continue;
}
if( (tabUsed & pLoop->maskSelf)!=0 ) continue;
pEnd = sWLB.pWC->a + sWLB.pWC->nTerm;
for(pTerm=sWLB.pWC->a; pTerm<pEnd; pTerm++){
if( (pTerm->prereqAll & pLoop->maskSelf)!=0 ){
if( !ExprHasProperty(pTerm->pExpr, EP_FromJoin)
|| pTerm->pExpr->iRightJoinTable!=pItem->iCursor
){
break;
}
}
}
if( pTerm<pEnd ) continue;
WHERETRACE(0xffff, ("-> drop loop %c not used\n", pLoop->cId));
notReady &= ~pLoop->maskSelf;
for(pTerm=sWLB.pWC->a; pTerm<pEnd; pTerm++){
if( (pTerm->prereqAll & pLoop->maskSelf)!=0 ){
pTerm->wtFlags |= TERM_CODED;
}
}
if( i!=pWInfo->nLevel-1 ){
int nByte = (pWInfo->nLevel-1-i) * sizeof(WhereLevel);
memmove(&pWInfo->a[i], &pWInfo->a[i+1], nByte);
}
pWInfo->nLevel--;
nTabList--;
}
notReady = whereOmitNoopJoin(pWInfo, notReady);
nTabList = pWInfo->nLevel;
assert( nTabList>0 );
}
#if defined(WHERETRACE_ENABLED)
if( sqlite3WhereTrace & 0x100 ){ /* Display all terms of the WHERE clause */
sqlite3DebugPrintf("---- WHERE clause at end of analysis:\n");