

SSC Rookie
Group: General Forum Members
Last Login: Friday, February 27, 2015 2:43 AM
Points: 27,
Visits: 28





Old Hand
Group: General Forum Members
Last Login: Thursday, September 22, 2016 8:01 AM
Points: 374,
Visits: 1,193


Abslolutely ridiculous example.
Bad advice.
This is the most inefficient way of calculating factorials.
At least if there was a warning that this is intended to show how recursion works along with a warning to novices that in the case of a factorial this definitely not the proper way of doing and why.




Forum Newbie
Group: General Forum Members
Last Login: Tuesday, August 31, 2010 12:01 PM
Points: 1,
Visits: 1





Forum Newbie
Group: General Forum Members
Last Login: Thursday, July 24, 2014 12:50 PM
Points: 4,
Visits: 11


A better solution with no limits.
Thanks to: http://2smart4school.com/tsqlstoredproceduretogetfactorialofagivennumber/
CREATE PROCEDURE Factorial (@num INT) AS BEGIN
DECLARE @fact int, @query varchar(255) SET @fact = 1 IF(@num = 0) BEGIN SET @fact = 1 END ELSE BEGIN WHILE(@num >0) BEGIN SET @fact = @fact * @num SET @num = @num 1 END END RETURN @fact END




SSCForever
Group: General Forum Members
Last Login: Today @ 12:17 PM
Points: 41,636,
Visits: 38,994


davidrudd (4/12/2013) A better solution with no limits.
Thanks to: http://2smart4school.com/tsqlstoredproceduretogetfactorialofagivennumber/
CREATE PROCEDURE Factorial (@num INT) AS BEGIN
DECLARE @fact int, @query varchar(255) SET @fact = 1 IF(@num = 0) BEGIN SET @fact = 1 END ELSE BEGIN WHILE(@num >0) BEGIN SET @fact = @fact * @num SET @num = @num 1 END END RETURN @fact END
Not quite true. That stored procedure is limited to a factorial of only 12 because of the INT datatype. Because it's a proc, it's difficult to use in a nonRBAR environment. And I'm not sure that I'd trust anyone's code that blatantly had an unused variable in it.
I guess I don't understand why people insist on recalculating that which will not change. For example, no matter how many times you calculate it, 170! will always return the same number. So why not calculate it just once and store it in a "helper" table?
Here's how to make a Factorial "helper" table.
===== Create the table with columns for N and N!.  This will prepopulate the values of N, as well. SELECT TOP 171 N = IDENTITY(INT,0,1), [N!] = CAST(0 AS FLOAT) INTO dbo.Factorial FROM sys.all_columns ; ===== Add the quintessential PK for max performance of future lookups ALTER TABLE dbo.Factorial ADD CONSTRAINT PK_Factorial PRIMARY KEY CLUSTERED (N) WITH FILLFACTOR = 100 ; ===== Declare a variable that well need to keep track of the previous product. DECLARE @Factorial FLOAT;
===== Update the table with factorials. UPDATE f SET @Factorial = [N!] = CASE WHEN N > 0 THEN @Factorial * N ELSE 1 END FROM dbo.Factorial f WITH (TABLOCKX, INDEX(1)) OPTION (MAXDOP 1) ; ===== Show our work SELECT * FROM dbo.Factorial ORDER BY N;
Then all you have to do is join to the factorial table for any number of rows in a set based fashion instead of recalculating the same thing over and over.
Jeff Moden "RBAR is pronounced "reebar" and is a "Modenism" for "RowByAgonizingRow".
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."
Helpful Links: How to post code problems How to post performance problems



