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Avoid manifesting a CTE (or other view) multiple times when it is possible to

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reuse the first manifestation.

FossilOrigin-Name: 9692f510803c9b9725abb687d7c10fbc0d5ed784479ec6f3fcc55925a87fe16d
This commit is contained in:
drh
2021-02-13 16:39:24 +00:00
parent e8f1490f55
commit 8794c68a35
5 changed files with 45 additions and 13 deletions
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8
src/select.c
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@@ -4593,6 +4593,7 @@ static int pushDownWhereTerms(
}
if( sqlite3ExprIsTableConstant(pWhere, iCursor) ){
nChng++;
pSubq->selFlags |= SF_PushDown;
while( pSubq ){
SubstContext x;
pNew = sqlite3ExprDup(pParse->db, pWhere, 0);
@@ -5765,6 +5766,8 @@ static struct SrcList_item *isSelfJoinView(
struct SrcList_item *pThis /* Search for prior reference to this subquery */
){
struct SrcList_item *pItem;
assert( pThis->pSelect!=0 );
if( pThis->pSelect->selFlags & SF_PushDown ) return 0;
for(pItem = pTabList->a; pItem<pThis; pItem++){
Select *pS1;
if( pItem->pSelect==0 ) continue;
@@ -5780,9 +5783,7 @@ static struct SrcList_item *isSelfJoinView(
** names in the same FROM clause. */
continue;
}
if( sqlite3ExprCompare(0, pThis->pSelect->pWhere, pS1->pWhere, -1)
|| sqlite3ExprCompare(0, pThis->pSelect->pHaving, pS1->pHaving, -1)
){
if( pItem->pSelect->selFlags & SF_PushDown ){
/* The view was modified by some other optimization such as
** pushDownWhereTerms() */
continue;
@@ -6203,6 +6204,7 @@ int sqlite3Select(
sqlite3TreeViewSelect(0, p, 0);
}
#endif
assert( pItem->pSelect && (pItem->pSelect->selFlags & SF_PushDown)!=0 );
}else{
SELECTTRACE(0x100,pParse,p,("Push-down not possible\n"));
}