Find last sunday

Question

How will you find last sunday of a month in sql 2000?

Answer 1

Here's the correct way, accounting for @@DATEFIRST

IF NOT EXISTS (SELECT * FROM sys.objects WHERE object_id = OBJECT_ID(N'[dbo].[fu_dtLastSundayInMonth]') AND type in (N'FN', N'IF', N'TF', N'FS', N'FT'))
BEGIN
    EXECUTE(N'CREATE FUNCTION [dbo].[fu_dtLastSundayInMonth]() RETURNS int BEGIN RETURN 0 END ')
END 
GO 



/*
SET DATEFIRST 3; -- Monday

WITH CTE AS (

    SELECT 1 AS i, CAST('20190101' AS datetime) AS mydate  
    UNION ALL 

    SELECT i+1 AS i, DATEADD(month, 1, CTE.mydate) AS mydate 
    FROM CTE WHERE i < 100 
)

SELECT -666 AS i, dbo.fu_dtLastSundayInMonth('17530101') AS lastSundayInMonth, dbo.fu_dtLastSundayInMonth('17530101') AS Control 

UNION ALL 

SELECT -666 AS i, dbo.fu_dtLastSundayInMonth('99991231') AS lastSundayInMonth, dbo.fu_dtLastSundayInMonth('99991231') AS Control 

UNION ALL 

SELECT 
     mydate 
    ,dbo.fu_dtLastSundayInMonth(mydate) AS lastSundayInMonth 
    ,dbo.fu_dtLastSundayInMonth(mydate) AS lastSundayInMonth 
    ,DATEADD(day,DATEDIFF(day,'19000107', DATEADD(MONTH, DATEDIFF(MONTH, 0, mydate, 30))/7*7,'19000107') AS Control 
FROM CTE 

*/


-- =====================================================================
-- Description:   Return date of last sunday in month
--                of the same year and month as @in_DateTime
-- =====================================================================
ALTER FUNCTION [dbo].[fu_dtLastSundayInMonth](@in_DateTime datetime )
RETURNS DateTime
AS
BEGIN
    -- Abrunden des Eingabedatums auf 00:00:00 Uhr
    DECLARE @dtReturnValue AS DateTime  
    -- 26.12.9999   SO
    IF @in_DateTime >= CAST('99991201' AS datetime) 
        RETURN CAST('99991226' AS datetime); 

    -- @dtReturnValue is now last day of month 
    SET @dtReturnValue = DATEADD 
        (
             DAY 
            ,-1
            ,DATEADD
            (
                 MONTH
                ,1
                ,CAST(CAST(YEAR(@in_DateTime) AS varchar(4)) + RIGHT('00' + CAST(MONTH(@in_DateTime) AS varchar(2)), 2) + '01' AS datetime) 
            )
        )
    ;

    -- SET DATEFIRST 1 -- Monday - Super easy ! 
    -- SET DATEFIRST != 1 - PHUK THIS ! 
    SET @dtReturnValue = DATEADD
                        (
                            day
                            ,
                             -
                             (

                                (
                                    -- DATEPART(WEEKDAY, @lastDayofMonth) -- with SET DATEFIRST 1 
                                    DATEPART(WEEKDAY, @dtReturnValue) + @@DATEFIRST - 2 % 7 + 1 
                                )
                                %7
                            )
                            , @dtReturnValue
    );

    RETURN @dtReturnValue; 
END


GO