public bool IsLeapYear(int year)
{
        if ((year < 1) || (year > 9999))
        {
            throw new ArgumentOutOfRangeException("year", "年份必須是從1至9999之間數字.");
        }
        if ((year % 4) != 0)
        {
            return false;
        }
        if ((year % 100) == 0)
        {
            return ((year % 400) == 0);
        }
        return true;
}

Public Function IsLeapYear(year As Integer) As Boolean
        If (year < 1) OrElse (year > 9999) Then
            Throw New ArgumentOutOfRangeException("year", "年份必須是從1至9999之間數字.")
        End If
        If (year Mod 4) <> 0 Then
            Return False
        End If
        If (year Mod 100) = 0 Then
            Return ((year Mod 400) = 0)
        End If
        Return True
End Function

udf_DaysInMonth_Ver2

CREATE FUNCTION [dbo].[udf_DaysInMonth]
(
    @Date DATETIME
)
RETURNS INT
AS
BEGIN
RETURN CASE WHEN MONTH(@Date) IN (1,3,5,7,8,10,12) THEN 31
            WHEN MONTH(@Date) IN (4,6,9,11) THEN 30
            ELSE CASE WHEN (YEAR(@Date) % 4 = 0 AND YEAR(@Date) % 100 <> 0) OR (YEAR(@Date) % 400  = 0)
                      THEN 29
                      ELSE 28
                 END
            END
END