How to create the greek orthodox easter calendar in sql server? - sql

Question

I am a newbie in SQL and i really need your help for my project. So, i had to create a master calendar table (which i have already created with the name "DimDate") but the problem is that i can't define right the function for the Easter Holidays in Greece.
I'm trying to create a function which will return the Easter Holidays (e.g Easter Sunday, Easter Monday, Good Friday) using the Meeus's Julian algorithm and not the Gregorian.
The function i have already tried, concerns the Gregorian calendar and as a result i get wrong dates for most of Easter Sundays. For example, for the year 2015, i see from the result of my query that the Easter Sunday was on 05/04/2015 (dd/MM/yyy) BUT the truth is that on 2015 the real date of Easter Sunday in Greece was 12/04/2015. And this is because i used the Gregorian algorithm as you can see below in the code i used.
CREATE FUNCTION dbo.GetEasterHolidays(#year INT)
RETURNS TABLE
WITH SCHEMABINDING
AS
RETURN
(
WITH x AS
(
SELECT [Date] = CONVERT(DATE, RTRIM(#year) + '0' + RTRIM([Month])
+ RIGHT('0' + RTRIM([Day]),2))
FROM (SELECT [Month], [Day] = DaysToSunday + 28 - (31 * ([Month] / 4))
FROM (SELECT [Month] = 3 + (DaysToSunday + 40) / 44, DaysToSunday
FROM (SELECT DaysToSunday = paschal - ((#year + #year / 4 + paschal - 13) % 7)
FROM (SELECT paschal = epact - (epact / 28)
FROM (SELECT epact = (24 + 19 * (#year % 19)) % 30)
AS epact) AS paschal) AS dts) AS m) AS d
)
SELECT [Date], HolidayName = 'Easter Sunday' FROM x
UNION ALL SELECT DATEADD(DAY,-2,[Date]), 'Good Friday' FROM x
UNION ALL SELECT DATEADD(DAY, 1,[Date]), 'Easter Monday' FROM x
);
--- Now 'updating' my "DimDate" calendar table---
;WITH x AS
(
SELECT d.[Date], d.IsHolidayEU, d.HolidayEU, h.HolidayName
FROM dbo.DimDate AS d
CROSS APPLY dbo.GetEasterHolidays(d.[Year]) AS h
WHERE d.[Date] = h.[Date]
)
UPDATE x SET IsHolidayEU = 1, HolidayEU = HolidayName;
I have searched the internet extensively and i found what i wanted but in HANA, not sql. I am confused since i tried to convert the HANA Code i found into sql but didn't manage it.
Also, here is the link from the HANA code i found, it contains 2 pictures.
I think i need to convert the second (image) code into sql server statements.
https://blogs.sap.com/2015/04/08/happy-easter-folks-easter-date-calculation/
Please help me if you can...and thank you in advance.
*Sorry for the looks of the code, i am new here, i couldn't find the way to make it better in order to be whole inside the "grey" area

Answer 1

It is a great function that works great at least until 2100.
In order to not have performance issues create a temp table with the given dates like this:
WITH estdates as
(SELECT c.fd EasterSunday
, c.[Year]
, DATEADD(dd,-2,c.fd) EasterFriday
, DATEADD(dd,1,c.fd) EasterMonday
FROM
(
SELECT dbo.UDF_GetEaster_Orthodox( ur.YR) fd,ur.YR [Year]
FROM
(
SELECT ROW_NUMBER() OVER (ORDER BY N1.N) +1999 AS YR
FROM (VALUES(1),(1),(1),(1),(1),(1),(1),(1)) AS N1(N)
CROSS JOIN (VALUES(1),(1),(1),(1),(1),(1),(1),(1)) AS N2(N)
) AS ur
) c
)
select *
into #EasterHolidays
from
(SELECT EasterFriday EasterHolidays FROM estdates d
UNION ALL
SELECT EasterMonday FROM estdates d ) a

Answer 2

I finally managed to get the right results with the following code.
The first function gives the Easter Sunday:
CREATE FUNCTION dbo.Easter_Orthodox22(#YEAR INT)
RETURNS DATE
AS
BEGIN
DECLARE #EasterMonth INT,
#EasterDay INT,
#Easter NVARCHAR(10),
#EYear VARCHAR(4),
#EMonth VARCHAR(2),
#EDay VARCHAR(2),
#EasterDate DATE,
#a INT,
#b INT,
#c INT,
#d INT,
#e INT;
SET #a = #YEAR%4;
SET #b = #YEAR%7;
SET #c = #YEAR%19;
SET #d = (19 * #c + 15)%30;
SET #e = (2 * #a + 4 * #b - #d +34)%7;
SET #EasterDay = (((#d + #e + 114)%31)+1);
SET #EasterMonth = CAST(((#d + #e + 114)/31) AS INT);
SET #EYear = CAST( #YEAR AS VARCHAR(4));
SET #EMonth = CAST( #EasterMonth AS VARCHAR(2));
SET #EDay = CAST( #EasterDay AS VARCHAR(2));
SET #Easter = CONCAT( CONCAT( #EYear, RIGHT( CONCAT('0', #EMonth),2)), RIGHT ( CONCAT('0', #EDay),2));
SET #EasterDate = CAST( #Easter AS DATE);
SET #EasterDate = DATEADD( day, 13, #EasterDate);
RETURN #EasterDate;
END
GO
Then, i created two more functions in order to find the Easter Monday and Great Friday:
CREATE FUNCTION dbo.GetEasterMonday2 (#YEAR INT)
RETURNS DATE
AS
BEGIN
RETURN (SELECT convert(date,convert(datetime,dbo.Easter_Orthodox2(#YEAR)) + 1))
END
GO
CREATE FUNCTION dbo.GetGoodFriday2 (#YEAR INT)
RETURNS DATE
AS
BEGIN
RETURN (SELECT convert(date,convert(datetime,dbo.Easter_Orthodox2(#YEAR)) - 2))
END
GO
But, now i am facing a different problem! A performance one, when i try to update my master calendar. I do the following in order to update the calendar:
UPDATE [dbo].[DimDate]
SET IsHolidayEU = 1,
HolidayEU = 'Easter Sunday'
WHERE [DATE] = dbo.Easter_Orthodox22(#CurrentYear)
UPDATE [dbo].[DimDate]
SET IsHolidayEU = 1,
HolidayEU = 'Good Friday'
WHERE [DATE] = dbo.GetGoodFriday2(#CurrentYear)
UPDATE [dbo].[DimDate]
SET IsHolidayEU = 1,
HolidayEU = 'Easter Monday'
WHERE [DATE] = dbo.GetEasterMonday2(#CurrentYear)
These Update expression are written inside a while loop inside my calendar code..I think that i should have used the "SCHEMABINDING" and/or "CROSS APPLY" with "with-query" that is exhibited in the primary code but don't know how to change my code into that in order to improve the performance..Any help appreciated guys!