Simple function to get beginning or end of month

Thu Apr 14, 2011 by Peter Larsson in optimization, sql-server-2008, algorithms, sql-server-2005, sql-server-2000

CREATE FUNCTION dbo.fnIsOnMonthEdge
(
    @theDate DATETIME
)
RETURNS SMALLINT
AS
BEGIN
    RETURN CASE @theDate
                WHEN '99991231' THEN 1
                ELSE DATEDIFF(MONTH, @theDate, DATEADD(DAY, 1, @theDate))
            END +
            CASE @theDate
                WHEN '17530101' THEN -1
                ELSE DATEDIFF(MONTH, @theDate, DATEADD(DAY, -1, @theDate))
            END
END