expression: fix issue that TimeIsNull is not compatible with MySQL

expression/builtin_op.go

@@ -799,8 +799,13 @@ func (c *isNullFunctionClass) getFunction(ctx sessionctx.Context, args []Express
 		sig = &builtinRealIsNullSig{bf}
 		sig.setPbCode(tipb.ScalarFuncSig_RealIsNull)
 	case types.ETDatetime:
-		sig = &builtinTimeIsNullSig{bf}
-		sig.setPbCode(tipb.ScalarFuncSig_TimeIsNull)
+		if mysql.HasNotNullFlag(args[0].GetType().Flag) {
+			sig = &builtinTimeIsNullSigOnNotNullCol{bf}
+			sig.setPbCode(tipb.ScalarFuncSig_TimeIsNullOnNotNullCol)
+		} else {
+			sig = &builtinTimeIsNullSig{bf}
+			sig.setPbCode(tipb.ScalarFuncSig_TimeIsNull)
+		}
 	case types.ETDuration:
 		sig = &builtinDurationIsNullSig{bf}
 		sig.setPbCode(tipb.ScalarFuncSig_DurationIsNull)
@@ -912,3 +917,18 @@ func (b *builtinTimeIsNullSig) evalInt(row chunk.Row) (int64, bool, error) {
 	_, isNull, err := b.args[0].EvalTime(b.ctx, row)
 	return evalIsNull(isNull, err)
 }
+
+type builtinTimeIsNullSigOnNotNullCol struct {
+	baseBuiltinFunc
+}
+
+func (b *builtinTimeIsNullSigOnNotNullCol) Clone() builtinFunc {
+	newSig := &builtinTimeIsNullSig{}
+	newSig.cloneFrom(&b.baseBuiltinFunc)
+	return newSig
+}
+
+func (b *builtinTimeIsNullSigOnNotNullCol) evalInt(row chunk.Row) (int64, bool, error) {
+	t, isNull, err := b.args[0].EvalTime(b.ctx, row)
+	return evalIsNull(isNull || t.IsZero(), err)
+}

expression/distsql_builtin.go

@@ -337,6 +337,8 @@ func getSignatureByPB(ctx sessionctx.Context, sigCode tipb.ScalarFuncSig, tp *ti
 		f = &builtinRealIsNullSig{base}
 	case tipb.ScalarFuncSig_TimeIsNull:
 		f = &builtinTimeIsNullSig{base}
+	case tipb.ScalarFuncSig_TimeIsNullOnNotNullCol:
+		f = &builtinTimeIsNullSigOnNotNullCol{base}
 	case tipb.ScalarFuncSig_StringIsNull:
 		f = &builtinStringIsNullSig{base}
 	case tipb.ScalarFuncSig_IntIsNull:

expression/integration_test.go

@@ -4398,3 +4398,28 @@ func (s *testIntegrationSuite) TestIssue10181(c *C) {
 	tk.MustExec(`insert into t values(9223372036854775807), (18446744073709551615)`)
 	tk.MustQuery(`select * from t where a > 9223372036854775807-0.5 order by a`).Check(testkit.Rows(`9223372036854775807`, `18446744073709551615`))
 }
+
+func (s *testIntegrationSuite) TestIssue9763(c *C) {
+	tk := testkit.NewTestKit(c, s.store)
+	tk.MustExec("use test")
+
+	tk.MustExec(`drop table if exists t1;`)
+	tk.MustExec(`CREATE TABLE t1 (a datetime not null);`)
+	tk.MustExec(`insert ignore into t1 values (0);`)
+	tk.MustQuery(`select * from t1 where a is null;`).Check(testkit.Rows(`0000-00-00 00:00:00`))
+
+	tk.MustExec(`drop table if exists t2;`)
+	tk.MustExec(`CREATE TABLE t2 (a date not null);`)
+	tk.MustExec(`insert ignore into t2 values (0);`)
+	tk.MustQuery(`select * from t2 where a is null;`).Check(testkit.Rows(`0000-00-00`))
+
+	tk.MustExec(`drop table if exists t3;`)
+	tk.MustExec(`CREATE TABLE t3 (a datetime);`)
+	tk.MustExec(`insert ignore into t3 values (0);`)
+	c.Assert(len(tk.MustQuery(`select * from t3 where a is null;`).Rows()), Equals, 0)
+
+	tk.MustExec(`drop table if exists t4;`)
+	tk.MustExec(`CREATE TABLE t4 (a date);`)
+	tk.MustExec(`insert ignore into t4 values (0);`)
+	c.Assert(len(tk.MustQuery(`select * from t4 where a is null;`).Rows()), Equals, 0)
+}