[release-22.0] fix sqlSelectLimit propagating to subqueries (#18716) (#18872)

Signed-off-by: ghostframe <[email protected]>
Co-authored-by: vitess-bot[bot] <108069721+vitess-bot[bot]@users.noreply.github.com>

Author: vitess-bot[bot]

go/test/endtoend/vtgate/misc_test.go

@@ -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", ``)

go/vt/sqlparser/normalizer.go

@@ -184,7 +184,7 @@ 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:
@@ -575,7 +575,7 @@ 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))}
 	}
 }