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The push-down optimization was being too aggressive such that it sometimes

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generated incorrect results.  Reinstate the restriction (4) (with
qualifications) that was removed by check-ins
[b5d3dd8cb0b1e4] and [dd568c27b1d765].

FossilOrigin-Name: f08c1731b0b1dddcba190b094a35306a159713d3db939330f73075ff1d72c81e
This commit is contained in:
drh
2018-03-27 15:13:43 +00:00
parent f900327ed8
commit 6a9b9527fa
4 changed files with 37 additions and 14 deletions
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20
src/select.c
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@@ -3857,8 +3857,9 @@ static int flattenSubquery(
** (3) The inner query has a LIMIT clause (since the changes to the WHERE
** close would change the meaning of the LIMIT).
**
** (4) (** This restriction was removed on 2018-03-21. It used to read:
** The inner query is the right operand of a LEFT JOIN. **)
** (4) The inner query is the right operand of a LEFT JOIN and the
** expression to be pushed down does not come from the ON clause
** on that LEFT JOIN.
**
** (5) The WHERE clause expression originates in the ON or USING clause
** of a LEFT JOIN where iCursor is not the right-hand table of that
@@ -3880,7 +3881,8 @@ static int pushDownWhereTerms(
Parse *pParse, /* Parse context (for malloc() and error reporting) */
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 */
int iCursor, /* Cursor number of the subquery */
int isLeftJoin /* True if pSubq is the right term of a LEFT JOIN */
){
Expr *pNew;
int nChng = 0;
@@ -3904,9 +3906,16 @@ static int pushDownWhereTerms(
return 0; /* restriction (3) */
}
while( pWhere->op==TK_AND ){
nChng += pushDownWhereTerms(pParse, pSubq, pWhere->pRight, iCursor);
nChng += pushDownWhereTerms(pParse, pSubq, pWhere->pRight,
iCursor, isLeftJoin);
pWhere = pWhere->pLeft;
}
if( isLeftJoin
&& (ExprHasProperty(pWhere,EP_FromJoin)==0
|| pWhere->iRightJoinTable!=iCursor)
){
return 0; /* restriction (4) */
}
if( ExprHasProperty(pWhere,EP_FromJoin) && pWhere->iRightJoinTable!=iCursor ){
return 0; /* restriction (5) */
}
@@ -5374,7 +5383,8 @@ int sqlite3Select(
** inside the subquery. This can help the subquery to run more efficiently.
*/
if( OptimizationEnabled(db, SQLITE_PushDown)
&& pushDownWhereTerms(pParse, pSub, p->pWhere, pItem->iCursor)
&& pushDownWhereTerms(pParse, pSub, p->pWhere, pItem->iCursor,
(pItem->fg.jointype & JT_OUTER)!=0)
){
#if SELECTTRACE_ENABLED
if( sqlite3SelectTrace & 0x100 ){