update date function to allow for zero time

Author: angelamayxie

enginetest/queries/function_queries.go

@@ -1839,7 +1839,6 @@ var FunctionQueryTests = []QueryTest{
 		ExpectedWarningsCount: 1,
 	},
 	{
-		// This is not a valid time string in MySQL, but we allow it
 		Query:    "select day('0000-00-00')",
 		Expected: []sql.Row{{0}},
 	},
@@ -1897,7 +1896,6 @@ var FunctionQueryTests = []QueryTest{
 		ExpectedWarningsCount: 1,
 	},
 	{
-		// This is not a valid time string in MySQL, but we allow it
 		Query:    "select dayofmonth('0000-00-00')",
 		Expected: []sql.Row{{0}},
 	},
@@ -1983,7 +1981,6 @@ var FunctionQueryTests = []QueryTest{
 		ExpectedWarningsCount: 1,
 	},
 	{
-		// This is not a valid time string in MySQL, but we allow it
 		Query:    "select month('0000-00-00')",
 		Expected: []sql.Row{{0}},
 	},
@@ -2153,7 +2150,6 @@ var FunctionQueryTests = []QueryTest{
 		ExpectedWarningsCount: 1,
 	},
 	{
-		// This is not a valid time string in MySQL, but we allow it
 		Query:    "select quarter('0000-00-00')",
 		Expected: []sql.Row{{0}},
 	},
@@ -2166,22 +2162,16 @@ var FunctionQueryTests = []QueryTest{
 		Expected: []sql.Row{{"0000-01-01"}},
 	},
 	{
-		Query:                 "select date('0000-00-00')",
-		Expected:              []sql.Row{{nil}},
-		ExpectedWarning:       mysql.ERTruncatedWrongValue,
-		ExpectedWarningsCount: 1,
+		Query:    "select date('0000-00-00')",
+		Expected: []sql.Row{{"0000-00-00"}},
 	},
 	{
-		Query:                 "select date(0)",
-		Expected:              []sql.Row{{nil}},
-		ExpectedWarning:       mysql.ERTruncatedWrongValue,
-		ExpectedWarningsCount: 1,
+		Query:    "select date(0)",
+		Expected: []sql.Row{{"0000-00-00"}},
 	},
 	{
-		Query:                 "select date(false)",
-		Expected:              []sql.Row{{nil}},
-		ExpectedWarning:       mysql.ERTruncatedWrongValue,
-		ExpectedWarningsCount: 1,
+		Query:    "select date(false)",
+		Expected: []sql.Row{{"0000-00-00"}},
 	},
 	{
 		Query:                 "select date(true)",

sql/expression/function/time.go

@@ -1309,10 +1309,13 @@ func (d *Date) Eval(ctx *sql.Context, row sql.Row) (interface{}, error) {
 	}
 
 	dateTime, ok := date.(time.Time)
-	if !ok || dateTime.Equal(types.ZeroTime) {
+	if !ok {
 		ctx.Warn(1292, "%s", types.ErrConvertingToTime.New(dateVal).Error())
 		return nil, nil
 	}
+	if dateTime.Equal(types.ZeroTime) {
+		return types.ZeroDateStr, nil
+	}
 
 	return dateTime.Format("2006-01-02"), nil
 }