expression: fix date_add interval month,year diffs from mysql (#8988)

expression/builtin_time.go

@@ -2632,7 +2632,7 @@ func (du *baseDateArithmitical) add(ctx sessionctx.Context, date types.Time, int
 
 	duration := time.Duration(dur)
 	goTime = goTime.Add(duration)
-	goTime = goTime.AddDate(int(year), int(month), int(day))
+	goTime = types.AddDate(year, month, day, goTime)
 
 	if goTime.Nanosecond() == 0 {
 		date.Fsp = 0
@@ -2658,7 +2658,7 @@ func (du *baseDateArithmitical) sub(ctx sessionctx.Context, date types.Time, int
 
 	duration := time.Duration(dur)
 	goTime = goTime.Add(duration)
-	goTime = goTime.AddDate(int(year), int(month), int(day))
+	goTime = types.AddDate(year, month, day, goTime)
 
 	if goTime.Nanosecond() == 0 {
 		date.Fsp = 0
@@ -5587,15 +5587,7 @@ func (b *builtinLastDaySig) evalTime(row chunk.Row) (types.Time, bool, error) {
 	if year == 0 && month == 0 && tm.Day() == 0 {
 		return types.Time{}, true, errors.Trace(handleInvalidTimeError(b.ctx, types.ErrIncorrectDatetimeValue.GenWithStackByArgs(arg.String())))
 	}
-	if month == 1 || month == 3 || month == 5 ||
-		month == 7 || month == 8 || month == 10 || month == 12 {
-		day = 31
-	} else if month == 2 {
-		day = 28
-		if tm.IsLeapYear() {
-			day = 29
-		}
-	}
+	day = types.GetLastDay(year, month)
 	ret := types.Time{
 		Time: types.FromDate(year, month, day, 0, 0, 0, 0),
 		Type: mysql.TypeDate,

expression/builtin_time_test.go

@@ -1656,6 +1656,55 @@ func (s *testEvaluatorSuite) TestDateArithFuncs(c *C) {
 	v, err = evalBuiltinFunc(f, chunk.Row{})
 	c.Assert(err, IsNil)
 	c.Assert(v.IsNull(), IsTrue)
+
+	testMonths := []struct {
+		input    string
+		months   int
+		expected string
+	}{
+		{"1900-01-31", 1, "1900-02-28"},
+		{"2000-01-31", 1, "2000-02-29"},
+		{"2016-01-31", 1, "2016-02-29"},
+		{"2018-07-31", 1, "2018-08-31"},
+		{"2018-08-31", 1, "2018-09-30"},
+		{"2018-07-31", 2, "2018-09-30"},
+		{"2016-01-31", 27, "2018-04-30"},
+		{"2000-02-29", 12, "2001-02-28"},
+		{"2000-11-30", 1, "2000-12-30"},
+	}
+
+	for _, test := range testMonths {
+		args = types.MakeDatums(test.input, test.months, "MONTH")
+		f, err = fcAdd.getFunction(s.ctx, s.datumsToConstants(args))
+		c.Assert(err, IsNil)
+		c.Assert(f, NotNil)
+		v, err = evalBuiltinFunc(f, chunk.Row{})
+		c.Assert(err, IsNil)
+		c.Assert(v.GetMysqlTime().String(), Equals, test.expected)
+	}
+
+	testYears := []struct {
+		input    string
+		year     int
+		expected string
+	}{
+		{"1899-02-28", 1, "1900-02-28"},
+		{"1901-02-28", -1, "1900-02-28"},
+		{"2000-02-29", 1, "2001-02-28"},
+		{"2001-02-28", -1, "2000-02-28"},
+		{"2004-02-29", 1, "2005-02-28"},
+		{"2005-02-28", -1, "2004-02-28"},
+	}
+
+	for _, test := range testYears {
+		args = types.MakeDatums(test.input, test.year, "YEAR")
+		f, err = fcAdd.getFunction(s.ctx, s.datumsToConstants(args))
+		c.Assert(err, IsNil)
+		c.Assert(f, NotNil)
+		v, err = evalBuiltinFunc(f, chunk.Row{})
+		c.Assert(err, IsNil)
+		c.Assert(v.GetMysqlTime().String(), Equals, test.expected)
+	}
 }
 
 func (s *testEvaluatorSuite) TestTimestamp(c *C) {

types/mytime.go

@@ -119,7 +119,56 @@ func (t MysqlTime) GoTime(loc *gotime.Location) (gotime.Time, error) {
 
 // IsLeapYear returns if it's leap year.
 func (t MysqlTime) IsLeapYear() bool {
-	return (t.year%4 == 0 && t.year%100 != 0) || t.year%400 == 0
+	return isLeapYear(t.year)
+}
+
+func isLeapYear(year uint16) bool {
+	return (year%4 == 0 && year%100 != 0) || year%400 == 0
+}
+
+var daysByMonth = [12]int{31, 28, 31, 30, 31, 30, 31, 31, 30, 31, 30, 31}
+
+// GetLastDay returns the last day of the month
+func GetLastDay(year, month int) int {
+	var day = 0
+	if month > 0 && month <= 12 {
+		day = daysByMonth[month-1]
+	}
+	if month == 2 && isLeapYear(uint16(year)) {
+		day = 29
+	}
+	return day
+}
+
+func getFixDays(year, month, day int, ot gotime.Time) int {
+	if (year != 0 || month != 0) && day == 0 {
+		od := ot.Day()
+		t := ot.AddDate(year, month, day)
+		td := t.Day()
+		if od != td {
+			tm := int(t.Month()) - 1
+			tMax := GetLastDay(t.Year(), tm)
+			dd := tMax - od
+			return dd
+		}
+	}
+	return 0
+}
+
+// AddDate fix gap between mysql and golang api
+// When we execute select date_add('2018-01-31',interval 1 month) in mysql we got 2018-02-28
+// but in tidb we got 2018-03-03.
+// Dig it and we found it's caused by golang api time.Date(year int, month Month, day, hour, min, sec, nsec int, loc *Location) Time ,
+// it says October 32 converts to November 1 ,it conflits with mysql.
+// See https://dev.mysql.com/doc/refman/5.7/en/date-and-time-functions.html#function_date-add
+func AddDate(year, month, day int64, ot gotime.Time) (nt gotime.Time) {
+	df := getFixDays(int(year), int(month), int(day), ot)
+	if df != 0 {
+		nt = ot.AddDate(int(year), int(month), df)
+	} else {
+		nt = ot.AddDate(int(year), int(month), int(day))
+	}
+	return nt
 }
 
 func calcTimeFromSec(to *MysqlTime, seconds, microseconds int) {

types/mytime_test.go

@@ -210,3 +210,21 @@ func (s *testMyTimeSuite) TestIsLeapYear(c *C) {
 		c.Assert(tt.T.IsLeapYear(), Equals, tt.Expect)
 	}
 }
+func (s *testMyTimeSuite) TestGetLastDay(c *C) {
+	tests := []struct {
+		year        int
+		month       int
+		expectedDay int
+	}{
+		{2000, 1, 31},
+		{2000, 2, 29},
+		{2000, 4, 30},
+		{1900, 2, 28},
+		{1996, 2, 29},
+	}
+
+	for _, t := range tests {
+		day := GetLastDay(t.year, t.month)
+		c.Assert(day, Equals, t.expectedDay)
+	}
+}