SQL Functions - factorial

Question

I am a beginner in SQL Functions. What is the best way to create a function for factorial in SQL Server- Say 10!

Answer 1

I know I'm a little late here, but it's worth noting that the recursive way that Martin posted does not work for 0.

This will (forgive me, I was having issues posting the code):

---

declare @target int=3;

WITH N AS
(SELECT 1 AS i, 
        1 AS f
 UNION ALL
 SELECT i+1,
        f*(i+1)
 FROM N
 WHERE  i < @target),
N0 AS
(SELECT f FROM N WHERE i=@target UNION SELECT 0)
SELECT MAX(f) FROM N0

And for the way, way faster version:

declare @target int=5;

WITH N AS
(SELECT 1 AS i, 
        1 AS f
 UNION ALL
 SELECT i+1,
        f*(i+1)
 FROM N
 WHERE i < @target),
N0 AS
(SELECT f FROM N WHERE i=@target UNION SELECT f=CASE WHEN @target=0 THEN 0 END)
SELECT f FROM N0
WHERE f>=0

This is much faster because I lose the MAX() function which, just like top 1, causes a DISTINCT sort.