Credits:
Author: Unknown
Date: Sometime over the last 2000 years
Description
Most public holiday dates fall on dates/days that can be calculated with simple absolute (Valentines Day = 14 Feb) or offset (Victoria Day = 3rd Monday in May) rules.
Easter Sunday calculation follows a more complex set of rules called Computus, a definition of which can be found on Wikipedia.
The algorithm for calculating this has been ported through many systems, and the TSQL code below is a representation suitable for SQL Server.
Code
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DROP FUNCTION [dbo].[udf_EasterSundayByYear]
GO
CREATE FUNCTION [dbo].[udf_EasterSundayByYear]
(@Year CHAR(4))
RETURNS SMALLDATETIME
AS
BEGIN
--http://aa.usno.navy.mil/faq/docs/easter.php
DECLARE
@c INT
, @n INT
, @k INT
, @i INT
, @j INT
, @l INT
, @m INT
, @d INT
, @Easter DATETIME
SET @c = (@Year / 100)
SET @n = @Year - 19 * (@Year / 19)
SET @k = (@c - 17) / 25
SET @i = @c - @c / 4 - ( @c - @k) / 3 + 19 * @n + 15
SET @i = @i - 30 * ( @i / 30 )
SET @i = @i - (@i / 28) * (1 - (@i / 28) * (29 / (@i + 1)) * ((21 - @n) / 11))
SET @j = @Year + @Year / 4 + @i + 2 - @c + @c / 4
SET @j = @j - 7 * (@j / 7)
SET @l = @i - @j
SET @m = 3 + (@l + 40) / 44
SET @d = @l + 28 - 31 * ( @m / 4 )
SET @Easter = (SELECT RIGHT('0' + CONVERT(VARCHAR(2),@m),2) + '/' + RIGHT('0' + CONVERT(VARCHAR(2),@d),2) + '/' + CONVERT(CHAR(4),@Year))
RETURN @Easter
END
--SELECT dbo.[udf_EasterSundayByYear] (2010)
--SELECT dbo.[udf_EasterSundayByYear] (2011)
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 Updating... Calculate date of Easter Sunday.sql (1k) Andy Hughes, Jun 21, 2012, 10:55 AM
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