types: extract month support 0 (pingcap#10116)

Author: WangXiangUSTC

types/time.go

@@ -1538,19 +1538,15 @@ func checkDatetimeType(t MysqlTime, allowZeroInDate, allowInvalidDate bool) erro
 
 // ExtractDatetimeNum extracts time value number from datetime unit and format.
 func ExtractDatetimeNum(t *Time, unit string) (int64, error) {
+	// TODO: Consider time_zone variable.
 	switch strings.ToUpper(unit) {
 	case "DAY":
 		return int64(t.Time.Day()), nil
 	case "WEEK":
 		week := t.Time.Week(0)
 		return int64(week), nil
 	case "MONTH":
-		// TODO: Consider time_zone variable.
-		t1, err := t.Time.GoTime(gotime.Local)
-		if err != nil {
-			return 0, errors.Trace(err)
-		}
-		return int64(t1.Month()), nil
+		return int64(t.Time.Month()), nil
 	case "QUARTER":
 		m := int64(t.Time.Month())
 		// 1 - 3 -> 1

types/time_test.go

@@ -1165,6 +1165,32 @@ func (s *testTimeSuite) TestExtractDatetimeNum(c *C) {
 	res, err = types.ExtractDatetimeNum(&in, "TEST_ERROR")
 	c.Assert(res, Equals, int64(0))
 	c.Assert(err, ErrorMatches, "invalid unit.*")
+
+	in = types.Time{
+		Time: types.FromDate(0000, 00, 00, 00, 00, 00, 0000),
+		Type: mysql.TypeTimestamp,
+		Fsp:  types.DefaultFsp,
+	}
+
+	res, err = types.ExtractDatetimeNum(&in, "day")
+	c.Assert(err, IsNil)
+	c.Assert(res, Equals, int64(0))
+
+	res, err = types.ExtractDatetimeNum(&in, "week")
+	c.Assert(err, IsNil)
+	c.Assert(res, Equals, int64(0))
+
+	res, err = types.ExtractDatetimeNum(&in, "MONTH")
+	c.Assert(err, IsNil)
+	c.Assert(res, Equals, int64(0))
+
+	res, err = types.ExtractDatetimeNum(&in, "QUARTER")
+	c.Assert(err, IsNil)
+	c.Assert(res, Equals, int64(0))
+
+	res, err = types.ExtractDatetimeNum(&in, "YEAR")
+	c.Assert(err, IsNil)
+	c.Assert(res, Equals, int64(0))
 }
 
 func (s *testTimeSuite) TestExtractDurationNum(c *C) {