expression: do not derive filters containing null sensitive functions…

… from outer join (#27067) (#27193)

expression/constant_propagation.go

@@ -146,7 +146,7 @@ func tryToReplaceCond(ctx sessionctx.Context, src *Column, tgt *Column, cond Exp
 			sf.FuncName.L == ast.If ||
 			sf.FuncName.L == ast.Case ||
 			sf.FuncName.L == ast.NullEQ) {
-		return false, false, cond
+		return false, true, cond
 	}
 	for idx, expr := range sf.GetArgs() {
 		if src.Equal(nil, expr) {

expression/integration_test.go

@@ -8251,3 +8251,21 @@ func (s *testIntegrationSuite) TestJiraSetInnoDBDefaultRowFormat(c *C) {
 	tk.MustQuery("SHOW VARIABLES LIKE 'innodb_file_format'").Check(testkit.Rows("innodb_file_format Barracuda"))
 	tk.MustQuery("SHOW VARIABLES LIKE 'innodb_large_prefix'").Check(testkit.Rows("innodb_large_prefix ON"))
 }
+
+func (s *testIntegrationSuite) TestConstPropNullFunctions(c *C) {
+	tk := testkit.NewTestKit(c, s.store)
+	tk.MustExec("use test")
+	tk.MustExec("drop table if exists t1, t2")
+	tk.MustExec("create table t1 (a integer)")
+	tk.MustExec("insert into t1 values (0), (1), (2), (3)")
+	tk.MustExec("create table t2 (a integer, b integer)")
+	tk.MustExec("insert into t2 values (0,1), (1,1), (2,1), (3,1)")
+	tk.MustQuery("select t1.* from t1 left join t2 on t2.a = t1.a where t1.a = ifnull(t2.b, 0)").Check(testkit.Rows("1"))
+
+	tk.MustExec("drop table if exists t1, t2")
+	tk.MustExec("create table t1 (i1 integer, c1 char)")
+	tk.MustExec("insert into t1 values (2, 'a'), (1, 'b'), (3, 'c'), (0, null);")
+	tk.MustExec("create table t2 (i2 integer, c2 char, f2 float)")
+	tk.MustExec("insert into t2 values (0, 'c', null), (1, null, 0.1), (3, 'b', 0.01), (2, 'q', 0.12), (null, 'a', -0.1), (null, null, null)")
+	tk.MustQuery("select * from t2 where t2.i2=((select count(1) from t1 where t1.i1=t2.i2))").Check(testkit.Rows("1 <nil> 0.1"))
+}