sql/expression: new date function

README.md

@@ -69,6 +69,7 @@ We support and actively test against certain third-party clients to ensure compa
 |`CONNECTION_ID()`|Return the current connection ID.|
 |`COUNT(expr)`| Returns a count of the number of non-NULL values of expr in the rows retrieved by a SELECT statement.|
 |`DAY(date)`|Synonym for DAYOFMONTH().|
+|`DATE(date)`|Returns the date part of the given date.|
 |`DAYOFMONTH(date)`|Return the day of the month (0-31).|
 |`DAYOFWEEK(date)`|Returns the day of the week of the given date.|
 |`DAYOFYEAR(date)`|Returns the day of the year of the given date.|

SUPPORTED.md

@@ -114,8 +114,10 @@
 - FROM_BASE64
 
 ## Time functions
+- DATE
 - DAY
 - WEEKDAY
+- DAYOFMONTH
 - DAYOFWEEK
 - DAYOFYEAR
 - HOUR

sql/expression/function/registry.go

@@ -33,6 +33,7 @@ var Defaults = []sql.Function{
 	sql.FunctionN{Name: "substring", Fn: NewSubstring},
 	sql.FunctionN{Name: "mid", Fn: NewSubstring},
 	sql.FunctionN{Name: "substr", Fn: NewSubstring},
+	sql.Function1{Name: "date", Fn: NewDate},
 	sql.Function1{Name: "year", Fn: NewYear},
 	sql.Function1{Name: "month", Fn: NewMonth},
 	sql.Function1{Name: "day", Fn: NewDay},

sql/expression/function/time.go

@@ -573,3 +573,39 @@ func (n *Now) Eval(*sql.Context, sql.Row) (interface{}, error) {
 func (n *Now) TransformUp(f sql.TransformExprFunc) (sql.Expression, error) {
 	return f(n)
 }
+
+// Date a function takes the DATE part out from a datetime expression.
+type Date struct {
+	expression.UnaryExpression
+}
+
+// NewDate returns a new Date node.
+func NewDate(date sql.Expression) sql.Expression {
+	return &Date{expression.UnaryExpression{Child: date}}
+}
+
+func (d *Date) String() string { return fmt.Sprintf("DATE(%s)", d.Child) }
+
+// Type implements the Expression interface.
+func (d *Date) Type() sql.Type { return sql.Text }
+
+// Eval implements the Expression interface.
+func (d *Date) Eval(ctx *sql.Context, row sql.Row) (interface{}, error) {
+	return getDatePart(ctx, d.UnaryExpression, row, func(v interface{}) interface{} {
+		if v == nil {
+			return nil
+		}
+
+		return v.(time.Time).Format("2006-01-02")
+	})
+}
+
+// TransformUp implements the sql.Expression interface.
+func (d *Date) TransformUp(f sql.TransformExprFunc) (sql.Expression, error) {
+	child, err := d.Child.TransformUp(f)
+	if err != nil {
+		return nil, err
+	}
+
+	return f(NewDate(child))
+}

sql/expression/function/time_test.go

@@ -354,3 +354,34 @@ func TestNow(t *testing.T) {
 	require.NoError(err)
 	require.Equal(date, result)
 }
+
+func TestDate(t *testing.T) {
+	f := NewDate(expression.NewGetField(0, sql.Text, "foo", false))
+	ctx := sql.NewEmptyContext()
+
+	testCases := []struct {
+		name     string
+		row      sql.Row
+		expected interface{}
+		err      bool
+	}{
+		{"null date", sql.NewRow(nil), nil, false},
+		{"invalid type", sql.NewRow([]byte{0, 1, 2}), nil, false},
+		{"date as string", sql.NewRow(stringDate), "2007-01-02", false},
+		{"date as time", sql.NewRow(time.Now()), time.Now().Format("2006-01-02"), false},
+		{"date as unix timestamp", sql.NewRow(int64(tsDate)), "2009-11-22", false},
+	}
+
+	for _, tt := range testCases {
+		t.Run(tt.name, func(t *testing.T) {
+			require := require.New(t)
+			val, err := f.Eval(ctx, tt.row)
+			if tt.err {
+				require.Error(err)
+			} else {
+				require.NoError(err)
+				require.Equal(tt.expected, val)
+			}
+		})
+	}
+}