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If terms of the WHERE clause require that the right table in a LEFT JOIN

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not be a null row, then simplify the LEFT JOIN into an ordinary JOIN.

FossilOrigin-Name: 5b7abecc7ab8ccbbb8cb5e0f672e67625c2555ad03442efbf34cb395f5bb71a8
This commit is contained in:
drh
2018-03-20 21:16:15 +00:00
parent f6e6f02308
commit 2589787c5a
7 changed files with 109 additions and 14 deletions
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40
src/select.c
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@@ -382,6 +382,28 @@ static void setJoinExpr(Expr *p, int iTable){
}
}
/* Undo the work of setJoinExpr(). In the expression tree p, convert every
** term that is marked with EP_FromJoin and iRightJoinTable==iTable into
** an ordinary term that omits the EP_FromJoin mark.
**
** This happens when a LEFT JOIN is simplified into an ordinary JOIN.
*/
static void unsetJoinExpr(Expr *p, int iTable){
while( p ){
if( ExprHasProperty(p, EP_FromJoin) && p->iRightJoinTable==iTable ){
ExprClearProperty(p, EP_FromJoin);
}
if( p->op==TK_FUNCTION && p->x.pList ){
int i;
for(i=0; i<p->x.pList->nExpr; i++){
unsetJoinExpr(p->x.pList->a[i].pExpr, iTable);
}
}
unsetJoinExpr(p->pLeft, iTable);
p = p->pRight;
}
}
/*
** This routine processes the join information for a SELECT statement.
** ON and USING clauses are converted into extra terms of the WHERE clause.
@@ -5175,13 +5197,29 @@ int sqlite3Select(
generateColumnNames(pParse, p);
}
/* Try to flatten subqueries in the FROM clause up into the main query
/* Try to various optimizations (flattening subqueries, and strength
** reduction of join operators) in the FROM clause up into the main query
*/
#if !defined(SQLITE_OMIT_SUBQUERY) || !defined(SQLITE_OMIT_VIEW)
for(i=0; !p->pPrior && i<pTabList->nSrc; i++){
struct SrcList_item *pItem = &pTabList->a[i];
Select *pSub = pItem->pSelect;
Table *pTab = pItem->pTab;
/* Convert LEFT JOIN into JOIN if there are terms of the right table
** of the LEFT JOIN used in the WHERE clause.
*/
if( (pItem->fg.jointype & JT_LEFT)!=0
&& sqlite3ExprImpliesNonNullRow(p->pWhere, pItem->iCursor)
&& OptimizationEnabled(db, SQLITE_SimplifyJoin)
){
SELECTTRACE(0x100,pParse,p,
("LEFT-JOIN simplifies to JOIN on term %d\n",i));
pItem->fg.jointype &= ~JT_LEFT;
unsetJoinExpr(p->pWhere, pItem->iCursor);
}
/* No futher action if this term of the FROM clause is no a subquery */
if( pSub==0 ) continue;
/* Catch mismatch in the declared columns of a view and the number of