function: implement NOW function

README.md

@@ -65,7 +65,7 @@ We support and actively test against certain third-party clients to ensure compa
 - `SUBSTRING(str, pos)`, `SUBSTRING(str, pos, len)` : Return a substring from the provided string.
 - `SUBSTR(str, pos)`, `SUBSTR(str, pos, len)` : Return a substring from the provided string.
 - `MID(str, pos)`, `MID(str, pos, len)` : Return a substring from the provided string.
-- Date and Timestamp functions: `YEAR(date)`, `MONTH(date)`, `DAY(date)`, `WEEKDAY(date)`, `HOUR(date)`, `MINUTE(date)`, `SECOND(date)`, `DAYOFWEEK(date)`, `DAYOFYEAR(date)`.
+- Date and Timestamp functions: `YEAR(date)`, `MONTH(date)`, `DAY(date)`, `WEEKDAY(date)`, `HOUR(date)`, `MINUTE(date)`, `SECOND(date)`, `DAYOFWEEK(date)`, `DAYOFYEAR(date)`, `NOW()`.
 - `ARRAY_LENGTH(json)`: If the json representation is an array, this function returns its size.
 - `SPLIT(str,sep)`: Receives a string and a separator and returns the parts of the string split by the separator as a JSON array of strings.
 - `CONCAT(...)`: Concatenate any group of fields into a single string.

SUPPORTED.md

@@ -120,3 +120,4 @@
 - MONTH
 - SECOND
 - YEAR
+- NOW

sql/expression/function/registry.go

@@ -68,4 +68,5 @@ var Defaults = sql.Functions{
 	"replace":       sql.Function3(NewReplace),
 	"ifnull":        sql.Function2(NewIfNull),
 	"nullif":        sql.Function2(NewNullIf),
+	"now":           sql.Function0(NewNow),
 }

sql/expression/function/time.go

@@ -327,3 +327,41 @@ var (
 	dayOfWeek = datePartFunc(func(t time.Time) int { return int(t.Weekday()) + 1 })
 	dayOfYear = datePartFunc((time.Time).YearDay)
 )
+
+type clock func() time.Time
+
+var defaultClock = time.Now
+
+// Now is a function that returns the current time.
+type Now struct {
+	clock
+}
+
+// NewNow returns a new Now node.
+func NewNow() sql.Expression {
+	return &Now{defaultClock}
+}
+
+// Type implements the sql.Expression interface.
+func (*Now) Type() sql.Type { return sql.Timestamp }
+
+func (*Now) String() string { return "NOW()" }
+
+// IsNullable implements the sql.Expression interface.
+func (*Now) IsNullable() bool { return false }
+
+// Resolved implements the sql.Expression interface.
+func (*Now) Resolved() bool { return true }
+
+// Children implements the sql.Expression interface.
+func (*Now) Children() []sql.Expression { return nil }
+
+// Eval implements the sql.Expression interface.
+func (n *Now) Eval(*sql.Context, sql.Row) (interface{}, error) {
+	return n.clock(), nil
+}
+
+// TransformUp implements the sql.Expression interface.
+func (n *Now) TransformUp(f sql.TransformExprFunc) (sql.Expression, error) {
+	return f(n)
+}

sql/expression/function/time_test.go

@@ -291,3 +291,16 @@ func TestTime_DayOfYear(t *testing.T) {
 		})
 	}
 }
+
+func TestNow(t *testing.T) {
+	require := require.New(t)
+	date := time.Date(2018, time.December, 2, 16, 25, 0, 0, time.Local)
+	clock := clock(func() time.Time {
+		return date
+	})
+	f := &Now{clock}
+
+	result, err := f.Eval(nil, nil)
+	require.NoError(err)
+	require.Equal(date, result)
+}