evaluator, parser: support UTC_DATE()

see issue: pingcap#236.

evaluator/builtin.go

@@ -62,6 +62,7 @@ var Funcs = map[string]Func{
 	"now":               {builtinNow, 0, 1},
 	"second":            {builtinSecond, 1, 1},
 	"sysdate":           {builtinSysDate, 0, 1},
+	"utc_date":          {builtinUTCDate, 0, 0},
 	"week":              {builtinWeek, 1, 2},
 	"weekday":           {builtinWeekDay, 1, 1},
 	"weekofyear":        {builtinWeekOfYear, 1, 1},

evaluator/builtin_time.go

@@ -390,6 +390,16 @@ func builtinCurrentTime(args []types.Datum, _ context.Context) (d types.Datum, e
 	return convertToDuration(d, fsp)
 }
 
+// See https://dev.mysql.com/doc/refman/5.7/en/date-and-time-functions.html#function_utc-date
+func builtinUTCDate(args []types.Datum, _ context.Context) (d types.Datum, err error) {
+	year, month, day := time.Now().Date()
+	t := mysql.Time{
+		Time: time.Date(year, month, day, 0, 0, 0, 0, time.UTC),
+		Type: mysql.TypeDate, Fsp: mysql.UnspecifiedFsp}
+	d.SetMysqlTime(t)
+	return d, nil
+}
+
 // See https://dev.mysql.com/doc/refman/5.7/en/date-and-time-functions.html#function_extract
 func builtinExtract(args []types.Datum, _ context.Context) (d types.Datum, err error) {
 	unit := args[0].GetString()

evaluator/builtin_time_test.go

@@ -316,6 +316,14 @@ func (s *testEvaluatorSuite) TestCurrentTime(c *C) {
 	c.Assert(err, NotNil)
 }
 
+func (s *testEvaluatorSuite) TestUTCDate(c *C) {
+	last := time.Now().UTC()
+	v, err := builtinUTCDate(types.MakeDatums(nil), nil)
+	c.Assert(err, IsNil)
+	n := v.GetMysqlTime()
+	c.Assert(n.String(), GreaterEqual, last.Format(mysql.DateFormat))
+}
+
 func (s *testEvaluatorSuite) TestDateArith(c *C) {
 	ctx := mock.NewContext()