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Nth occurence of a day in a month/year

By Biplov Dan, 2009/08/21

There is general problem in business world to get a particular day of a month at nth occurrence. For example to get the 3rd Monday of feb 2009 where 3rd represents the nth occurance of Monday.

The getDateAtNthOccurence function can be used in such case.

-- =============================================
-- Author: Biplov Kumar Dan
-- Create date: 12-Aug-2009
-- Description: To get date for nth occurence of a day in a month and year
-- SELECT dbo.getDateAtNthOccurence('01/Feb/2012',4,5)
-- =============================================
CREATE FUNCTION dbo.getDateAtNthOccurence
(
@inputDate DATETIME,
@day TINYINT, -- 1:Sunday, 2:Monday, 3:Tuesday, 4:Wednesday, 5:Thrusday, 6:Friday, 7:Saturday
@occurAt TINYINT -- 1:First, 2:Second, 3:Third, 4:Fourth, >4:Last
)
RETURNS DATETIME
AS
BEGIN

DECLARE @counter TINYINT, 
@firstDate DATETIME,
@lastDate DATETIME,
@retDate DATETIME

SELECT @counter = 1, @firstDate = DATEADD(dd,-(DAY(@inputDate)-1),@inputDate), @lastDate = DATEADD(dd,-1,DATEADD(MONTH,1,@firstDate))

WHILE @firstDate<=@lastDate 
BEGIN

IF(DATEPart(dw , @firstDate )=@day) and @counter<=@occurAt
BEGIN
SELECT @retDate = @firstDate,@counter = @counter+1
END

SET @firstDate = DATEADD(DAY,1,@firstDate)
END

-- Return the result of the function
RETURN @retDate

END
GO

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