diff --git a/expression/integration_test.go b/expression/integration_test.go
index 238e038dcaeaa..aa4f920e094d2 100755
--- a/expression/integration_test.go
+++ b/expression/integration_test.go
@@ -6763,3 +6763,53 @@ func (s *testIntegrationSerialSuite) TestIssue19045(c *C) {
 	tk.MustExec(`insert into t(a) values('101'),('101');`)
 	tk.MustQuery(`select  ( SELECT t1.a FROM  t1,  t2 WHERE t1.b = t2.a AND  t2.b = '03' AND t1.c = a.a) invode from t a ;`).Check(testkit.Rows("a011", "a011"))
 }
+<<<<<<< HEAD
+=======
+
+func (s *testIntegrationSerialSuite) TestIssue19116(c *C) {
+	collate.SetNewCollationEnabledForTest(true)
+	defer collate.SetNewCollationEnabledForTest(false)
+
+	tk := testkit.NewTestKit(c, s.store)
+	tk.MustExec("set names utf8mb4 collate utf8mb4_general_ci;")
+	tk.MustQuery("select collation(concat(1 collate `binary`));").Check(testkit.Rows("binary"))
+	tk.MustQuery("select coercibility(concat(1 collate `binary`));").Check(testkit.Rows("0"))
+	tk.MustQuery("select collation(concat(NULL,NULL));").Check(testkit.Rows("binary"))
+	tk.MustQuery("select coercibility(concat(NULL,NULL));").Check(testkit.Rows("6"))
+	tk.MustQuery("select collation(concat(1,1));").Check(testkit.Rows("utf8mb4_general_ci"))
+	tk.MustQuery("select coercibility(concat(1,1));").Check(testkit.Rows("4"))
+	tk.MustQuery("select collation(1);").Check(testkit.Rows("binary"))
+	tk.MustQuery("select coercibility(1);").Check(testkit.Rows("5"))
+	tk.MustQuery("select coercibility(1=1);").Check(testkit.Rows("5"))
+}
+
+func (s *testIntegrationSerialSuite) TestIssue17063(c *C) {
+	collate.SetNewCollationEnabledForTest(true)
+	defer collate.SetNewCollationEnabledForTest(false)
+
+	tk := testkit.NewTestKit(c, s.store)
+	tk.MustExec(`use test;`)
+	tk.MustExec(`drop table if exists t;`)
+	tk.MustExec("create table t(a char, b char) collate utf8mb4_general_ci;")
+	tk.MustExec(`insert into t values('a', 'b');`)
+	tk.MustExec(`insert into t values('a', 'B');`)
+	tk.MustQuery(`select * from t where if(a='x', a, b) = 'b';`).Check(testkit.Rows("a b", "a B"))
+	tk.MustQuery(`select collation(if(a='x', a, b)) from t;`).Check(testkit.Rows("utf8mb4_general_ci", "utf8mb4_general_ci"))
+	tk.MustQuery(`select coercibility(if(a='x', a, b)) from t;`).Check(testkit.Rows("2", "2"))
+	tk.MustQuery(`select collation(lag(b, 1, 'B') over w) from t window w as (order by b);`).Check(testkit.Rows("utf8mb4_general_ci", "utf8mb4_general_ci"))
+	tk.MustQuery(`select coercibility(lag(b, 1, 'B') over w) from t window w as (order by b);`).Check(testkit.Rows("2", "2"))
+}
+
+func (s *testIntegrationSuite) TestIssue19504(c *C) {
+	tk := testkit.NewTestKit(c, s.store)
+	tk.MustExec("use test")
+	tk.MustExec("drop table if exists t1;")
+	tk.MustExec("create table t1 (c_int int, primary key (c_int));")
+	tk.MustExec("insert into t1 values (1), (2), (3);")
+	tk.MustExec("drop table if exists t2;")
+	tk.MustExec("create table t2 (c_int int, primary key (c_int));")
+	tk.MustExec("insert into t2 values (1);")
+	tk.MustQuery("select (select count(c_int) from t2 where c_int = t1.c_int) c1, (select count(1) from t2 where c_int = t1.c_int) c2 from t1;").
+		Check(testkit.Rows("1 1", "0 0", "0 0"))
+}
+>>>>>>> 27ea908... planner: reset not null flag when Apply convert to Join (#19567)
diff --git a/planner/core/rule_decorrelate.go b/planner/core/rule_decorrelate.go
index 7027a44f78994..c92029d7f08e4 100644
--- a/planner/core/rule_decorrelate.go
+++ b/planner/core/rule_decorrelate.go
@@ -175,9 +175,19 @@ func (s *decorrelateSolver) optimize(ctx context.Context, p LogicalPlan) (Logica
 					outerCol.RetType = first.RetTp
 					outerColsInSchema = append(outerColsInSchema, outerCol)
 				}
-				newAggFuncs = append(newAggFuncs, agg.AggFuncs...)
-				agg.AggFuncs = newAggFuncs
 				apply.SetSchema(expression.MergeSchema(expression.NewSchema(outerColsInSchema...), innerPlan.Schema()))
+				resetNotNullFlag(apply.schema, outerPlan.Schema().Len(), apply.schema.Len())
+
+				for i, aggFunc := range agg.AggFuncs {
+					if idx := apply.schema.ColumnIndex(aggFunc.Args[0].(*expression.Column)); idx != -1 {
+						desc, err := aggregation.NewAggFuncDesc(agg.ctx, agg.AggFuncs[i].Name, []expression.Expression{apply.schema.Columns[idx]}, false)
+						if err != nil {
+							return nil, err
+						}
+						newAggFuncs = append(newAggFuncs, desc)
+					}
+				}
+				agg.AggFuncs = newAggFuncs
 				np, err := s.optimize(ctx, p)
 				if err != nil {
 					return nil, err