# Thinking outside the box

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## Fast easter day function

CREATE FUNCTION dbo.fnGetEasterDate
(
@Year SMALLINT
)
RETURNS DATE
AS
BEGIN
RETURN (
SELECT DATEADD(DAY, DATEDIFF(DAY, 0, CONVERT(DATETIME, CAST(@Year AS CHAR(4)) + BaseDate, 112)) / 7 * 7, 6)
FROM    (
SELECT CASE @Year % 19
WHEN  0 THEN '0415'
WHEN  1 THEN '0404'
WHEN  2 THEN '0324'
WHEN  3 THEN '0412'
WHEN  4 THEN '0401'
WHEN  5 THEN '0419'
WHEN  6 THEN '0409'
WHEN  7 THEN '0329'
WHEN  8 THEN '0417'
WHEN  9 THEN '0406'
WHEN 10 THEN '0326'
WHEN 11 THEN '0414'
WHEN 12 THEN '0403'
WHEN 13 THEN '0323'
WHEN 14 THEN '0411'
WHEN 15 THEN '0331'
WHEN 16 THEN '0418'
WHEN 17 THEN '0408'
WHEN 18 THEN '0328'
ELSE NULL
END
WHERE   @Year BETWEEN 1900 AND 9999
) AS d(BaseDate)
)
END

Print | posted on Wednesday, September 08, 2010 3:30 PM | Filed Under [ Optimization SQL Server 2008 Algorithms SQL Server 2005 SQL Server 2000 ]

## #re: Fast easter day function

Hi,

Maybe its me, but the / 7 * 7 is a 0 operation, it could be left out.

ciao.
1/17/2011 12:33 AM | iStan

## #re: Fast easter day function

You are completely right. It is you.

I am not sure, but it seems to me you are forgetting about integer division.
The first division by 7 ignores the decimal part in the result. Later, when multiplying with 7 you get a result which is the nearest lower value [than the original] that also is a tuple of 7.

//Peso
1/17/2011 9:45 AM |
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