Creating a UDF that will Accept Seeding for Rand() - sql

Question

I am getting the follow error when trying to create the following function:
Error 1 SQL80001: Incorrect syntax near 'RETURN SELECT CAST( RAND(
#offset * #seed )* #max as int ) + 1'
What am I doing wrongly?
CREATE FUNCTION [dbo].[fn_RandomInt]( #offset int, #seed int, #max int )
RETURNS INT
AS
RETURN
SELECT CAST( RAND( #offset * #seed )* #max as int ) + 1
Is it possible to create a UDF that will accept a SEED into the Rand() function?

Answer 1

Correct syntax to create a function would be:
CREATE FUNCTION [dbo].[fn_RandomInt]( #offset int, #seed int, #max int )
RETURNS INT
AS
begin
RETURN CAST( RAND( #offset * #seed )* #max as int ) + 1
end
GO
But then you're going to get the error:
Msg 443, Level 16, State 1, Procedure fn_RandomInt, Line 5 Invalid use
of a side-effecting operator 'rand' within a function.
This is because you can't put indeterminate functions inside a UDF. Your functions can use views or procedures that use indeterminate functions though for some reason, so you could create a stored procedure with an output variable that returns the value of the rand function and use it. You could also just send the output of a rand function to the function and use it instead. Like:
select dbo.fn_RandomInt(10, rand(#seed), 20)
Also, if you're trying to get your function to return a random number between #offset and #max, then your formula will not work. You'd want something more like:
CAST(#offset + RAND(#seed) * (#offset-#max+1) as int)

Answer 2

You can get the reason it wont work with this syntax which will give you this error.
CREATE FUNCTION [dbo].[fn_RandomInt]( #offset int, #seed int, #max int )
RETURNS INT
AS
BEGIN
DECLARE #v_offset INT, #v_seed INT, #v_max INT, #result INT
SELECT #result = CAST(RAND( #v_offset * #v_seed ) * #v_max as int ) + 1
RETURN #result
END
It will give you this error -
Msg 443, Level 16, State 1, Procedure RandFn, Line 7
Invalid use of a side-effecting operator ‘rand’ within a function
You can look here for help but you will need to do something different either way since you want to feed RAND() arguments, so the view idea wouldn't work.
http://blog.sqlauthority.com/2012/11/20/sql-server-using-rand-in-user-defined-functions-udf/