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Make the value of an explicit LIMIT clause on a scalar sub-query available to xBestIndex for simple "LIMIT 0" and "LIMIT 1" queries.

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FossilOrigin-Name: 33b6a63caafccc61b3193714911cd8b5dd9b7f1798054b8c7845b23688d531f2
This commit is contained in:
dan
2025-07-03 15:32:27 +00:00
parent c525e6e817
commit 0e6e05d4d5
4 changed files with 37 additions and 23 deletions
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26
src/expr.c
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@@ -3896,17 +3896,23 @@ int sqlite3CodeSubselect(Parse *pParse, Expr *pExpr){
VdbeComment((v, "Init EXISTS result"));
}
if( pSel->pLimit ){
/* The subquery already has a limit. If the pre-existing limit is X
** then make the new limit X<>0 so that the new limit is either 1 or 0 */
sqlite3 *db = pParse->db;
pLimit = sqlite3Expr(db, TK_INTEGER, "0");
if( pLimit ){
pLimit->affExpr = SQLITE_AFF_NUMERIC;
pLimit = sqlite3PExpr(pParse, TK_NE,
sqlite3ExprDup(db, pSel->pLimit->pLeft, 0), pLimit);
/* The subquery already has a limit. If the pre-existing limit X is
** not already integer value 1 or 0, then make the new limit X<>0 so that
** the new limit is either 1 or 0 */
Expr *pLeft = pSel->pLimit->pLeft;
if( ExprHasProperty(pLeft, EP_IntValue)==0
|| (pLeft->u.iValue!=1 && pLeft->u.iValue!=0)
){
sqlite3 *db = pParse->db;
pLimit = sqlite3Expr(db, TK_INTEGER, "0");
if( pLimit ){
pLimit->affExpr = SQLITE_AFF_NUMERIC;
pLimit = sqlite3PExpr(pParse, TK_NE,
sqlite3ExprDup(db, pLeft, 0), pLimit);
}
sqlite3ExprDeferredDelete(pParse, pLeft);
pSel->pLimit->pLeft = pLimit;
}
sqlite3ExprDeferredDelete(pParse, pSel->pLimit->pLeft);
pSel->pLimit->pLeft = pLimit;
}else{
/* If there is no pre-existing limit add a limit of 1 */
pLimit = sqlite3Expr(pParse->db, TK_INTEGER, "1");