planner: fix correctness of the correlated predicate push down for cte (

pingcap#43759)

close pingcap#43645

planner/core/integration_test.go

@@ -6819,3 +6819,18 @@ func TestIssue41273(t *testing.T) {
 			"IndexMerge"),
 	)
 }
+
+func TestIssue43645(t *testing.T) {
+	store, clean := testkit.CreateMockStore(t)
+	defer clean()
+	tk := testkit.NewTestKit(t, store)
+
+	tk.MustExec("use test")
+	tk.MustExec("CREATE TABLE t1(id int,col1 varchar(10),col2 varchar(10),col3 varchar(10));")
+	tk.MustExec("CREATE TABLE t2(id int,col1 varchar(10),col2 varchar(10),col3 varchar(10));")
+	tk.MustExec("INSERT INTO t1 values(1,NULL,NULL,null),(2,NULL,NULL,null),(3,NULL,NULL,null);")
+	tk.MustExec("INSERT INTO t2 values(1,'a','aa','aaa'),(2,'b','bb','bbb'),(3,'c','cc','ccc');")
+
+	rs := tk.MustQuery("WITH tmp AS (SELECT t2.* FROM t2) select (SELECT tmp.col1 FROM tmp WHERE tmp.id=t1.id ) col1, (SELECT tmp.col2 FROM tmp WHERE tmp.id=t1.id ) col2, (SELECT tmp.col3 FROM tmp WHERE tmp.id=t1.id ) col3 from t1;")
+	rs.Sort().Check(testkit.Rows("a aa aaa", "b bb bbb", "c cc ccc"))
+}

planner/core/rule_predicate_push_down.go

@@ -941,13 +941,26 @@ func (p *LogicalCTE) PredicatePushDown(predicates []expression.Expression, opt *
 	if !p.isOuterMostCTE {
 		return predicates, p.self
 	}
-	if len(predicates) == 0 {
+	pushedPredicates := make([]expression.Expression, len(predicates))
+	copy(pushedPredicates, predicates)
+	// The filter might change the correlated status of the cte.
+	// We forbid the push down that makes the change for now.
+	// Will support it later.
+	if !p.cte.IsInApply {
+		for i := len(pushedPredicates) - 1; i >= 0; i-- {
+			if len(expression.ExtractCorColumns(pushedPredicates[i])) == 0 {
+				continue
+			}
+			pushedPredicates = append(pushedPredicates[0:i], pushedPredicates[i+1:]...)
+		}
+	}
+	if len(pushedPredicates) == 0 {
 		p.cte.pushDownPredicates = append(p.cte.pushDownPredicates, expression.NewOne())
 		return predicates, p.self
 	}
 	newPred := make([]expression.Expression, 0, len(predicates))
-	for i := range predicates {
-		newPred = append(newPred, predicates[i].Clone())
+	for i := range pushedPredicates {
+		newPred = append(newPred, pushedPredicates[i].Clone())
 		ResolveExprAndReplace(newPred[i], p.cte.ColumnMap)
 	}
 	p.cte.pushDownPredicates = append(p.cte.pushDownPredicates, expression.ComposeCNFCondition(p.ctx, newPred...))