implementing quarter() function

sql/expression/function/registry.go

@@ -176,6 +176,7 @@ var BuiltIns = []sql.Function{
 	sql.Function0{Name: "pi", Fn: NewPi},
 	sql.Function2{Name: "pow", Fn: NewPower},
 	sql.Function2{Name: "power", Fn: NewPower},
+	sql.Function1{Name: "quarter", Fn: NewQuarter},
 	sql.Function1{Name: "radians", Fn: NewRadians},
 	sql.FunctionN{Name: "rand", Fn: NewRand},
 	sql.FunctionN{Name: "regexp_like", Fn: NewRegexpLike},

sql/expression/function/time.go

@@ -115,6 +115,60 @@ func (y *Year) WithChildren(children ...sql.Expression) (sql.Expression, error)
 	return NewYear(children[0]), nil
 }
 
+type Quarter struct {
+	expression.UnaryExpression
+}
+
+var _ sql.FunctionExpression = (*Quarter)(nil)
+var _ sql.CollationCoercible = (*Quarter)(nil)
+
+// NewQuarter creates a new Month UDF.
+func NewQuarter(date sql.Expression) sql.Expression {
+	return &Quarter{expression.UnaryExpression{Child: date}}
+}
+
+// FunctionName implements sql.FunctionExpression
+func (q *Quarter) FunctionName() string {
+	return "quarter"
+}
+
+// Description implements sql.FunctionExpression
+func (q *Quarter) Description() string {
+	return "returns the quarter of the given date."
+}
+
+func (q *Quarter) String() string { return fmt.Sprintf("%s(%s)", q.FunctionName(), q.Child) }
+
+// Type implements the Expression interface.
+func (q *Quarter) Type() sql.Type { return types.Int32 }
+
+// CollationCoercibility implements the interface sql.CollationCoercible.
+func (q *Quarter) CollationCoercibility(ctx *sql.Context) (collation sql.CollationID, coercibility byte) {
+	return sql.Collation_binary, 5
+}
+
+// Eval implements the Expression interface.
+func (q *Quarter) Eval(ctx *sql.Context, row sql.Row) (interface{}, error) {
+	mon, err := getDatePart(ctx, q.UnaryExpression, row, month)
+	if err != nil {
+		return nil, err
+	}
+
+	if mon == nil {
+		return nil, nil
+	}
+
+	return (mon.(int32)-1)/3 + 1, nil
+}
+
+// WithChildren implements the Expression interface.
+func (q *Quarter) WithChildren(children ...sql.Expression) (sql.Expression, error) {
+	if len(children) != 1 {
+		return nil, sql.ErrInvalidChildrenNumber.New(q, len(children), 1)
+	}
+	return NewQuarter(children[0]), nil
+}
+
 // Month is a function that returns the month of a date.
 type Month struct {
 	expression.UnaryExpression

sql/expression/function/time_test.go

@@ -92,6 +92,127 @@ func TestTime_Month(t *testing.T) {
 	}
 }
 
+func TestTime_Quarter(t *testing.T) {
+	ctx := sql.NewEmptyContext()
+	f := NewQuarter(expression.NewGetField(0, types.LongText, "foo", false))
+
+	testCases := []struct {
+		name     string
+		row      sql.Row
+		expected interface{}
+		err      bool
+	}{
+		{
+			name:     "null date",
+			row:      sql.NewRow(nil),
+			expected: nil,
+		},
+		{
+			name:     "1",
+			row:      sql.NewRow(1),
+			expected: int32(1),
+		},
+		{
+			name:     "1.1",
+			row:      sql.NewRow(1.1),
+			expected: int32(1),
+		},
+		{
+			name:     "invalid type",
+			row:      sql.NewRow([]byte{0, 1, 2}),
+			expected: int32(1),
+		},
+		{
+			name:     "date as string",
+			row:      sql.NewRow(stringDate),
+			expected: int32(1),
+		},
+		{
+			name:     "another date as string",
+			row:      sql.NewRow("2008-08-01"),
+			expected: int32(3),
+		},
+		{
+			name:     "january",
+			row:      sql.NewRow("2008-01-01"),
+			expected: int32(1),
+		},
+		{
+			name:     "february",
+			row:      sql.NewRow("2008-02-01"),
+			expected: int32(1),
+		},
+		{
+			name:     "march",
+			row:      sql.NewRow("2008-03-01"),
+			expected: int32(1),
+		},
+		{
+			name:     "april",
+			row:      sql.NewRow("2008-04-01"),
+			expected: int32(2),
+		},
+		{
+			name:     "may",
+			row:      sql.NewRow("2008-05-01"),
+			expected: int32(2),
+		},
+		{
+			name:     "june",
+			row:      sql.NewRow("2008-06-01"),
+			expected: int32(2),
+		},
+		{
+			name:     "july",
+			row:      sql.NewRow("2008-07-01"),
+			expected: int32(3),
+		},
+		{
+			name:     "august",
+			row:      sql.NewRow("2008-08-01"),
+			expected: int32(3),
+		},
+		{
+			name:     "septemeber",
+			row:      sql.NewRow("2008-09-01"),
+			expected: int32(3),
+		},
+		{
+			name:     "october",
+			row:      sql.NewRow("2008-10-01"),
+			expected: int32(4),
+		},
+		{
+			name:     "november",
+			row:      sql.NewRow("2008-11-01"),
+			expected: int32(4),
+		},
+		{
+			name:     "december",
+			row:      sql.NewRow("2008-12-01"),
+			expected: int32(4),
+		},
+		{
+			name:     "date as time",
+			row:      sql.NewRow(time.Now()),
+			expected: int32(time.Now().UTC().Month()),
+		},
+	}
+
+	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)
+			}
+		})
+	}
+}
+
 func TestTime_Day(t *testing.T) {
 	ctx := sql.NewEmptyContext()
 	f := NewDay(expression.NewGetField(0, types.LongText, "foo", false))