expression: fix issue that timestampadd is not compatible with Mysql (pingcap#10314)

Author: qw4990

expression/builtin_time.go

@@ -5649,13 +5649,30 @@ func (b *builtinTimestampAddSig) evalString(row chunk.Row) (string, bool, error)
 	default:
 		return "", true, errors.Trace(types.ErrInvalidTimeFormat.GenWithStackByArgs(unit))
 	}
-	r := types.Time{Time: types.FromGoTime(tb), Type: mysql.TypeDatetime, Fsp: fsp}
+	r := types.Time{Time: types.FromGoTime(tb), Type: b.resolveType(arg.Type, unit), Fsp: fsp}
 	if err = r.Check(b.ctx.GetSessionVars().StmtCtx); err != nil {
 		return "", true, errors.Trace(handleInvalidTimeError(b.ctx, err))
 	}
 	return r.String(), false, nil
 }
 
+func (b *builtinTimestampAddSig) resolveType(typ uint8, unit string) uint8 {
+	// The approach below is from MySQL.
+	// The field type for the result of an Item_date function is defined as
+	// follows:
+	//
+	//- If first arg is a MYSQL_TYPE_DATETIME result is MYSQL_TYPE_DATETIME
+	//- If first arg is a MYSQL_TYPE_DATE and the interval type uses hours,
+	//	minutes, seconds or microsecond then type is MYSQL_TYPE_DATETIME.
+	//- Otherwise the result is MYSQL_TYPE_STRING
+	//	(This is because you can't know if the string contains a DATE, MYSQL_TIME
+	//	or DATETIME argument)
+	if typ == mysql.TypeDate && (unit == "HOUR" || unit == "MINUTE" || unit == "SECOND" || unit == "MICROSECOND") {
+		return mysql.TypeDatetime
+	}
+	return typ
+}
+
 type toDaysFunctionClass struct {
 	baseFunctionClass
 }

expression/integration_test.go

@@ -1300,6 +1300,18 @@ func (s *testIntegrationSuite) TestTimeBuiltin(c *C) {
 	result.Check(testkit.Rows("2017-01-18 12:39:50.123 2017-01-18 12:39:50.999"))
 	result = tk.MustQuery("select timestamp('2003-12-31', '01:01:01.01'), timestamp('2003-12-31 12:34', '01:01:01.01')," +
 		" timestamp('2008-12-31','00:00:00.0'), timestamp('2008-12-31 00:00:00.000');")
+
+	tk.MustQuery(`select timestampadd(second, 1, cast("2001-01-01" as date))`).Check(testkit.Rows("2001-01-01 00:00:01"))
+	tk.MustQuery(`select timestampadd(hour, 1, cast("2001-01-01" as date))`).Check(testkit.Rows("2001-01-01 01:00:00"))
+	tk.MustQuery(`select timestampadd(day, 1, cast("2001-01-01" as date))`).Check(testkit.Rows("2001-01-02"))
+	tk.MustQuery(`select timestampadd(month, 1, cast("2001-01-01" as date))`).Check(testkit.Rows("2001-02-01"))
+	tk.MustQuery(`select timestampadd(year, 1, cast("2001-01-01" as date))`).Check(testkit.Rows("2002-01-01"))
+	tk.MustQuery(`select timestampadd(second, 1, cast("2001-01-01" as datetime))`).Check(testkit.Rows("2001-01-01 00:00:01"))
+	tk.MustQuery(`select timestampadd(hour, 1, cast("2001-01-01" as datetime))`).Check(testkit.Rows("2001-01-01 01:00:00"))
+	tk.MustQuery(`select timestampadd(day, 1, cast("2001-01-01" as datetime))`).Check(testkit.Rows("2001-01-02 00:00:00"))
+	tk.MustQuery(`select timestampadd(month, 1, cast("2001-01-01" as datetime))`).Check(testkit.Rows("2001-02-01 00:00:00"))
+	tk.MustQuery(`select timestampadd(year, 1, cast("2001-01-01" as datetime))`).Check(testkit.Rows("2002-01-01 00:00:00"))
+
 	result.Check(testkit.Rows("2003-12-31 01:01:01.01 2003-12-31 13:35:01.01 2008-12-31 00:00:00.0 2008-12-31 00:00:00.000"))
 	result = tk.MustQuery("select timestamp('2003-12-31', 1), timestamp('2003-12-31', -1);")
 	result.Check(testkit.Rows("2003-12-31 00:00:01 2003-12-30 23:59:59"))