SQL Factorial Function to Calculate Factorial of an Integer in SQL Server
In SQL Server, developers can use SQL factorial function given in this tutorial to calculate factorial for a given integer value.
For mathematical factorial calculation of an integer input value in SQL Server, sqlFactorial() userdefined function can be used as shown in the SQL tutorial.
If you don't already have a numbers table in your database, you can use following SQL codes to calculate factorial value of an input integer value.
 let's calculate 6 factorial
declare @factorial_number int = 6
declare @factorial_calculated bigint = 1
select top (@factorial_number)
@factorial_calculated = @factorial_calculated * ROW_NUMBER() over (order by id)
from sys.sysobjects order by id
select @factorial_calculated  result, factorial of @factorial_number
Let's see the results
On the other hand, if you have a numbers table in your SQL Server database the above code can be converted into a more readable SQL script as follows:
 let's calculate 10 factorial
declare @factorial_number int = 6
declare @factorial_calculated bigint = 1
select @factorial_calculated = @factorial_calculated * i from dbo.NumbersTable(1,@factorial_number,1)
select @factorial_calculated  (@factorial_number) factorial
SQL programmers can check SQL tutorial Create Numbers Table in SQL Server for dbo.NumbersTable() table valued function codes
Here is the output for 10! calculation (10 factorial calculation) in SQL Server for programmers.
Of course it is easier to convert the second method into a SQL factorial function to calculate factorial values easily.
create function sqlFactorial (@int int)
returns int
begin
declare @factorial bigint = 1
select @factorial = @factorial * i from dbo.NumbersTable(1,@int,1)
return @factorial
end
go
select
dbo.sqlFactorial(0) [0 factorial],
dbo.sqlFactorial(1) [1 factorial],
dbo.sqlFactorial(5) [5 factorial],
dbo.sqlFactorial(6) [6 factorial]
Here is how SQL programmers can use sqlFactorial userdefined function (UDF) to calculate factorial value of an input positive integer value.
