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Make handling of LIMIT clauses in correlated sub-queries on virtual tables more efficient.

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dan
2025-07-03 14:28:47 +00:00
parent 1ff6f19d8b
commit c525e6e817
4 changed files with 92 additions and 12 deletions
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20
src/whereexpr.c
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@@ -1652,7 +1652,7 @@ static void whereAddLimitExpr(
**
** 1. The SELECT statement has a LIMIT clause, and
** 2. The SELECT statement is not an aggregate or DISTINCT query, and
** 3. The SELECT statement has exactly one object in its from clause, and
** 3. The SELECT statement has exactly one object in its FROM clause, and
** that object is a virtual table, and
** 4. There are no terms in the WHERE clause that will not be passed
** to the virtual table xBestIndex method.
@@ -1689,8 +1689,22 @@ void SQLITE_NOINLINE sqlite3WhereAddLimit(WhereClause *pWC, Select *p){
** (leftCursor==iCsr) test below. */
continue;
}
if( pWC->a[ii].leftCursor!=iCsr ) return;
if( pWC->a[ii].prereqRight!=0 ) return;
if( pWC->a[ii].leftCursor==iCsr && pWC->a[ii].prereqRight==0 ) continue;
/* If this term has a parent with exactly one child, and the parent will
** be passed through to xBestIndex, then this term can be ignored. */
if( pWC->a[ii].iParent>=0 ){
WhereTerm *pParent = &pWC->a[ pWC->a[ii].iParent ];
if( pParent->leftCursor==iCsr
&& pParent->prereqRight==0
&& ALWAYS(pParent->nChild==1)
){
continue;
}
}
/* This term will not be passed through. Do not add a LIMIT clause. */
return;
}
/* Check condition (5). Return early if it is not met. */