[SQL] Get Number of Days in a Month Function

REATE FUNCTION [dbo].[GetDaysInMonth] ( @pDate DATETIME )
RETURNS INT
AS
BEGIN

   RETURN CASE WHEN MONTH(@pDate) IN (1, 3, 5, 7, 8, 10, 12) THEN 31
               WHEN MONTH(@pDate) IN (4, 6, 9, 11) THEN 30
               ELSE CASE WHEN (YEAR(@pDate) % 4    = 0 AND
                               YEAR(@pDate) % 100 != 0) OR
                              (YEAR(@pDate) % 400  = 0)
                         THEN 29
                         ELSE 28
                    END
          END

END
GO