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fix sqlSelectLimit propagating to subqueries #18716

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Merged
harshit-gangal merged 1 commit into from
Nov 5, 2025
Merged

fix sqlSelectLimit propagating to subqueries #18716

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7 changes: 7 additions & 0 deletions go/test/endtoend/vtgate/misc_test.go
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Original file line number Diff line number Diff line change
Expand Up @@ -528,6 +528,13 @@ func TestSQLSelectLimit(t *testing.T) {
utils.AssertMatches(t, conn, "select uid, msg from t7_xxhash order by uid", `[[VARCHAR("1") VARCHAR("a")] [VARCHAR("2") VARCHAR("b")]]`)
utils.AssertMatches(t, conn, "(select uid, msg from t7_xxhash order by uid)", `[[VARCHAR("1") VARCHAR("a")] [VARCHAR("2") VARCHAR("b")]]`)
utils.AssertMatches(t, conn, "select uid, msg from t7_xxhash order by uid limit 4", `[[VARCHAR("1") VARCHAR("a")] [VARCHAR("2") VARCHAR("b")] [VARCHAR("3") NULL] [VARCHAR("4") VARCHAR("a")]]`)

// Don't LIMIT subqueries
utils.AssertMatches(t, conn, "select count(*) from (select uid, msg from t7_xxhash order by uid) as subquery", `[[INT64(6)]]`)
utils.AssertMatches(t, conn, "select count(*) from (select 1 union all select 2 union all select 3) as subquery", `[[INT64(3)]]`)

utils.AssertMatches(t, conn, "select 1 union all select 2 union all select 3", `[[INT64(1)] [INT64(2)]]`)

/*
planner does not support query with order by in union query. without order by the results are not deterministic for testing purpose
utils.AssertMatches(t, conn, "select uid, msg from t7_xxhash union all select uid, msg from t7_xxhash order by uid", ``)
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4 changes: 2 additions & 2 deletions go/vt/sqlparser/normalizer.go
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Original file line number Diff line number Diff line change
Expand Up @@ -186,7 +186,7 @@ func (nz *normalizer) walkDown(node, _ SQLNode) bool {
nz.inDerived++
case *Select:
nz.inSelect++
if nz.selectLimit > 0 && node.Limit == nil {
if nz.selectLimit > 0 && node.Limit == nil && nz.inSelect == 1 {
node.Limit = &Limit{Rowcount: NewIntLiteral(strconv.Itoa(nz.selectLimit))}
}
case *AliasedExpr:
Expand Down Expand Up @@ -591,7 +591,7 @@ func shouldRewriteDatabaseFunc(in Statement) bool {

// rewriteUnion sets the SELECT limit for UNION statements if not already set.
func (nz *normalizer) rewriteUnion(node *Union) {
if nz.selectLimit > 0 && node.Limit == nil {
if nz.selectLimit > 0 && node.Limit == nil && nz.inSelect == 0 {
node.Limit = &Limit{Rowcount: NewIntLiteral(strconv.Itoa(nz.selectLimit))}
}
}
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