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 Posted Friday, November 29, 2013 6:08 AM
 Mr or Mrs. 500 Group: General Forum Members Last Login: Wednesday, April 16, 2014 12:52 AM Points: 588, Visits: 1,004
 I have an existing function on my DB which is used for date manipulations.Please explain how this function works. `ALTER FUNCTION [dbo].[ExplodeDates](@startdate datetime, @enddate datetime)returns table asreturn (with N0 as (SELECT 1 as n UNION ALL SELECT 1),N1 as (SELECT 1 as n FROM N0 t1, N0 t2),N2 as (SELECT 1 as n FROM N1 t1, N1 t2),N3 as (SELECT 1 as n FROM N2 t1, N2 t2),N4 as (SELECT 1 as n FROM N3 t1, N3 t2),N5 as (SELECT 1 as n FROM N4 t1, N4 t2),N6 as (SELECT 1 as n FROM N5 t1, N5 t2),nums as (SELECT ROW_NUMBER() OVER (ORDER BY (SELECT 1)) as num FROM N6)SELECT DATEADD(day,num-1,@startdate) as thedateFROM numsWHERE num <= DATEDIFF(day,@startdate,@enddate) + 1`
Post #1518531
 Posted Friday, November 29, 2013 6:21 AM
 SSC-Addicted Group: General Forum Members Last Login: Friday, April 18, 2014 6:52 AM Points: 470, Visits: 823
 This function is using Tally Table approach to generate calendar date between the @startDate And @EndDateif you want to understand properly then using this post from Stefan Krzywicki "Tally Table Uses - Part I" http://www.sqlservercentral.com/articles/Tally+Table/70735/
Post #1518535
 Posted Friday, November 29, 2013 7:07 AM
 SSCertifiable Group: General Forum Members Last Login: Thursday, April 17, 2014 9:33 AM Points: 6,754, Visits: 12,854
 Run the following code, query by query. If you're still unsure, post back.`WITH N0 as (SELECT 1 as n UNION ALL SELECT 1) -- 2 rows,N1 as (SELECT 1 as n FROM N0 t1, N0 t2) -- 4 rowsSELECT * FROM N1;WITH N0 as (SELECT 1 as n UNION ALL SELECT 1) -- 2 rows,N1 as (SELECT 1 as n FROM N0 t1, N0 t2) -- 4 rowsSELECT ROW_NUMBER() OVER (ORDER BY (SELECT NULL)) as num FROM N1;WITH N0 as (SELECT 1 as n UNION ALL SELECT 1) -- 2 rows,N1 as (SELECT 1 as n FROM N0 t1, N0 t2) -- 4 rows,nums AS (SELECT ROW_NUMBER() OVER (ORDER BY (SELECT NULL)) as num FROM N1)SELECT DATEADD(day,num, GETDATE()) FROM nums;` “Write the query the simplest way. If through testing it becomes clear that the performance is inadequate, consider alternative query forms.” - Gail ShawFor fast, accurate and documented assistance in answering your questions, please read this article.Understanding and using APPLY, (I) and (II) Paul White Hidden RBAR: Triangular Joins / The "Numbers" or "Tally" Table: What it is and how it replaces a loop Jeff ModenExploring Recursive CTEs by Example Dwain Camps
Post #1518548
 Posted Friday, November 29, 2013 7:09 AM
 SSCertifiable Group: General Forum Members Last Login: Thursday, April 17, 2014 9:33 AM Points: 6,754, Visits: 12,854
 Note that you don't need CTE N6:`DECLARE @startdate DATE, @enddate DATESET @startdate = '00010101'SET @enddate = '99990101';with N0 as (SELECT 1 as n UNION ALL SELECT 1) -- 2 rows,N1 as (SELECT 1 as n FROM N0 t1, N0 t2) -- 4 rows,N2 as (SELECT 1 as n FROM N1 t1, N1 t2) -- 16 rows,N3 as (SELECT 1 as n FROM N2 t1, N2 t2) -- 256 rows,N4 as (SELECT 1 as n FROM N3 t1, N3 t2) -- 65,536 rows,N5 as (SELECT 1 as n FROM N4 t1, N4 t2) -- 4,294,967,296 rows--,N6 as (SELECT 1 as n FROM N5 t1, N5 t2) -- 18,446,744,073,709,551,616 rows!!,nums as (SELECT ROW_NUMBER() OVER (ORDER BY (SELECT 1)) as num FROM N5)SELECT DATEADD(day,num-1,@startdate) as thedateFROM numsWHERE num <= DATEDIFF(day, @startdate, @enddate) + 1` “Write the query the simplest way. If through testing it becomes clear that the performance is inadequate, consider alternative query forms.” - Gail ShawFor fast, accurate and documented assistance in answering your questions, please read this article.Understanding and using APPLY, (I) and (II) Paul White Hidden RBAR: Triangular Joins / The "Numbers" or "Tally" Table: What it is and how it replaces a loop Jeff ModenExploring Recursive CTEs by Example Dwain Camps
Post #1518550
 Posted Friday, November 29, 2013 2:05 PM
 SSC-Dedicated Group: General Forum Members Last Login: Today @ 8:53 AM Points: 35,983, Visits: 30,273
 Not that many people would notice but you can get the code to be almost a third faster by eliminating the (-1) subtraction. Last but not least, the simplification actually instills a guarantee that you won't have an accidental overrun sometimes caused by the very rare but annoying delay as to when the WHERE clause is executed when you join the results of this function in an external query (Itzik Ben-Gan published that correction to his code just a couple of days after he first published the cascading CTE method used here).` CREATE FUNCTION dbo.ExplodeDates ( @pStartDate DATETIME ,@pEndDate DATETIME )RETURNS TABLE WITH SCHEMABINDING AS RETURN WITH E1(N) AS ( SELECT 1 UNION ALL SELECT 1 UNION ALL SELECT 1 UNION ALL SELECT 1 UNION ALL SELECT 1 UNION ALL SELECT 1 UNION ALL SELECT 1 UNION ALL SELECT 1 UNION ALL SELECT 1 UNION ALL SELECT 1 ), E7(N) AS (SELECT 1 FROM E1 a, E1 b, E1 c, E1 d, E1 e, E1 f, E1 g) SELECT TheDate = @pStartDate UNION ALL --This eliminates the need for subtraction on the Row_Number SELECT TOP (DATEDIFF(dd,@pStartDate,@pEndDate)) --and addition here TheDate = DATEADD(dd,ROW_NUMBER() OVER (ORDER BY (SELECT NULL)),@pStartDate) FROM E7;` --Jeff Moden"RBAR is pronounced "ree-bar" and is a "Modenism" for "Row-By-Agonizing-Row".First step towards the paradigm shift of writing Set Based code: Stop thinking about what you want to do to a row... think, instead, of what you want to do to a column." "Change is inevitable. Change for the better is not." -- 04 August 2013(play on words) "Just because you CAN do something in T-SQL, doesn't mean you SHOULDN'T." --22 Aug 2013Helpful Links:How to post code problemsHow to post performance problems
Post #1518596
 Posted Monday, December 02, 2013 2:57 AM
 SSCertifiable Group: General Forum Members Last Login: Thursday, April 17, 2014 9:33 AM Points: 6,754, Visits: 12,854
 Jeff Moden (11/29/2013)Not that many people would notice but you can get the code to be almost a third faster by eliminating the (-1) subtraction. Last but not least, the simplification actually instills a guarantee that you won't have an accidental overrun sometimes caused by the very rare but annoying delay as to when the WHERE clause is executed when you join the results of this function in an external query (Itzik Ben-Gan published that correction to his code just a couple of days after he first published the cascading CTE method used here).` CREATE FUNCTION dbo.ExplodeDates ( @pStartDate DATETIME ,@pEndDate DATETIME )RETURNS TABLE WITH SCHEMABINDING AS RETURN WITH E1(N) AS ( SELECT 1 UNION ALL SELECT 1 UNION ALL SELECT 1 UNION ALL SELECT 1 UNION ALL SELECT 1 UNION ALL SELECT 1 UNION ALL SELECT 1 UNION ALL SELECT 1 UNION ALL SELECT 1 UNION ALL SELECT 1 ), E7(N) AS (SELECT 1 FROM E1 a, E1 b, E1 c, E1 d, E1 e, E1 f, E1 g) SELECT TheDate = @pStartDate UNION ALL --This eliminates the need for subtraction on the Row_Number SELECT TOP (DATEDIFF(dd,@pStartDate,@pEndDate)) --and addition here TheDate = DATEADD(dd,ROW_NUMBER() OVER (ORDER BY (SELECT NULL)),@pStartDate) FROM E7;`How are you demonstrating the difference, Jeff? The results of a quick test show the opposite, but not by very much:`DECLARE @startdate DATE, @enddate DATE, @Blackhole DATE;SET @startdate = '00010101'SET @enddate = '99991231';PRINT '==Slow inline tally table==';PRINT CHAR(10)+'--Subtraction--';SET STATISTICS TIME ON;with N0 as (SELECT 1 as n UNION ALL SELECT 1) -- 2 rows,N1 as (SELECT 1 as n FROM N0 t1, N0 t2) -- 4 rows,N2 as (SELECT 1 as n FROM N1 t1, N1 t2) -- 16 rows,N3 as (SELECT 1 as n FROM N2 t1, N2 t2) -- 256 rows,N4 as (SELECT 1 as n FROM N3 t1, N3 t2) -- 65,536 rows,N5 as (SELECT 1 as n FROM N4 t1, N4 t2) -- 4,294,967,296 rows,nums as (SELECT ROW_NUMBER() OVER (ORDER BY (SELECT 1)) as num FROM N5)SELECT @Blackhole = thedate FROM ( SELECT thedate = DATEADD(day,num-1,@startdate) FROM nums WHERE num <= DATEDIFF(day, @startdate, @enddate) + 1) d;SET STATISTICS TIME OFF;PRINT CHAR(10)+'--UNION--';SET STATISTICS TIME ON;with N0 as (SELECT 1 as n UNION ALL SELECT 1) -- 2 rows,N1 as (SELECT 1 as n FROM N0 t1, N0 t2) -- 4 rows,N2 as (SELECT 1 as n FROM N1 t1, N1 t2) -- 16 rows,N3 as (SELECT 1 as n FROM N2 t1, N2 t2) -- 256 rows,N4 as (SELECT 1 as n FROM N3 t1, N3 t2) -- 65,536 rows,N5 as (SELECT 1 as n FROM N4 t1, N4 t2) -- 4,294,967,296 rows,nums as (SELECT ROW_NUMBER() OVER (ORDER BY (SELECT 1)) as num FROM N5)SELECT @Blackhole = thedate FROM ( SELECT thedate = @startdate UNION ALL SELECT DATEADD(day,num,@startdate) FROM nums WHERE num <= DATEDIFF(day, @startdate, @enddate)) d;SET STATISTICS TIME OFF;PRINT CHAR(10)+CHAR(10)+'==Fast IBG inline tally table==';PRINT CHAR(10)+'--Subtraction--';SET STATISTICS TIME ON;WITH E1(N) AS ( SELECT 1 UNION ALL SELECT 1 UNION ALL SELECT 1 UNION ALL SELECT 1 UNION ALL SELECT 1 UNION ALL SELECT 1 UNION ALL SELECT 1 UNION ALL SELECT 1 UNION ALL SELECT 1 UNION ALL SELECT 1 ), E7(N) AS (SELECT 1 FROM E1 a, E1 b, E1 c, E1 d, E1 e, E1 f, E1 g)SELECT @Blackhole = thedate FROM ( SELECT TOP (1+DATEDIFF(dd,@StartDate,@EndDate)) TheDate = DATEADD(dd,ROW_NUMBER() OVER (ORDER BY (SELECT NULL))-1,@StartDate) FROM E7) d;SET STATISTICS TIME OFF;PRINT CHAR(10)+'--UNION--';SET STATISTICS TIME ON;WITH E1(N) AS ( SELECT 1 UNION ALL SELECT 1 UNION ALL SELECT 1 UNION ALL SELECT 1 UNION ALL SELECT 1 UNION ALL SELECT 1 UNION ALL SELECT 1 UNION ALL SELECT 1 UNION ALL SELECT 1 UNION ALL SELECT 1 ), E7(N) AS (SELECT 1 FROM E1 a, E1 b, E1 c, E1 d, E1 e, E1 f, E1 g)SELECT @Blackhole = thedate FROM ( SELECT TheDate = @StartDate UNION ALL --This eliminates the need for subtraction on the Row_Number SELECT TOP (DATEDIFF(dd,@StartDate,@EndDate)) --and addition here TheDate = DATEADD(dd,ROW_NUMBER() OVER (ORDER BY (SELECT NULL)),@StartDate) FROM E7) d;SET STATISTICS TIME OFF;PRINT '=================================================================================';` “Write the query the simplest way. If through testing it becomes clear that the performance is inadequate, consider alternative query forms.” - Gail ShawFor fast, accurate and documented assistance in answering your questions, please read this article.Understanding and using APPLY, (I) and (II) Paul White Hidden RBAR: Triangular Joins / The "Numbers" or "Tally" Table: What it is and how it replaces a loop Jeff ModenExploring Recursive CTEs by Example Dwain Camps
Post #1518809

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