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Update the omit-table-from-left-join optimization so that it can omit tables

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from the middle of the join as well as the end.

FossilOrigin-Name: 618ca9fe53d8d2d7b4f368e6ee404d5fceeecac0d689f32ab62af8a6cbb37401
This commit is contained in:
dan
2017-11-21 19:22:45 +00:00
parent 62a83d262a
commit 41203c6cf1
4 changed files with 111 additions and 22 deletions
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65
src/where.c
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@@ -4677,35 +4677,73 @@ WhereInfo *sqlite3WhereBegin(
}
}
#endif
/* Attempt to omit tables from the join that do not effect the result */
/* 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:
**
** 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 USING (t1.ipk=t2.ipk)
** LEFT JOIN t3 USING (t1.ipk=t3.ipk)
**
** or from:
**
** SELECT DISTINCT v1, v3 FROM t1
** LEFT JOIN t2
** LEFT JOIN t3 USING (t1.ipk=t3.ipk)
*/
if( pWInfo->nLevel>=2
&& pResultSet!=0
&& pResultSet!=0 /* guarantees condition (1) above */
&& OptimizationEnabled(db, SQLITE_OmitNoopJoin)
){
int i;
Bitmask tabUsed = sqlite3WhereExprListUsage(pMaskSet, pResultSet);
if( sWLB.pOrderBy ){
tabUsed |= sqlite3WhereExprListUsage(pMaskSet, sWLB.pOrderBy);
}
while( pWInfo->nLevel>=2 ){
for(i=pWInfo->nLevel-1; i>=1; i--){
WhereTerm *pTerm, *pEnd;
pLoop = pWInfo->a[pWInfo->nLevel-1].pWLoop;
if( (pWInfo->pTabList->a[pLoop->iTab].fg.jointype & JT_LEFT)==0 ) break;
struct SrcList_item *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
){
break;
continue;
}
if( (tabUsed & pLoop->maskSelf)!=0 ) break;
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
&& !ExprHasProperty(pTerm->pExpr, EP_FromJoin)
){
break;
if( (pTerm->prereqAll & pLoop->maskSelf)!=0 ){
if( !ExprHasProperty(pTerm->pExpr, EP_FromJoin)
|| pTerm->pExpr->iRightJoinTable!=pItem->iCursor
){
break;
}
}
}
if( pTerm<pEnd ) break;
if( pTerm<pEnd ) continue;
WHERETRACE(0xffff, ("-> drop loop %c not used\n", pLoop->cId));
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--;
}
@@ -4990,7 +5028,8 @@ void sqlite3WhereEnd(WhereInfo *pWInfo){
addr = sqlite3VdbeAddOp1(v, OP_IfPos, pLevel->iLeftJoin); VdbeCoverage(v);
assert( (ws & WHERE_IDX_ONLY)==0 || (ws & WHERE_INDEXED)!=0 );
if( (ws & WHERE_IDX_ONLY)==0 ){
sqlite3VdbeAddOp1(v, OP_NullRow, pTabList->a[i].iCursor);
assert( pLevel->iTabCur==pTabList->a[pLevel->iFrom].iCursor );
sqlite3VdbeAddOp1(v, OP_NullRow, pLevel->iTabCur);
}
if( (ws & WHERE_INDEXED)
|| ((ws & WHERE_MULTI_OR) && pLevel->u.pCovidx)