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

If you are okay with an approximation, use Stirling's Approximation.

create table #temp (value int)

insert into #temp values (5),(6),(7),(8)

select 
    value,
    sqrt(2*3.14*value)*power((value/2.718),value) --stirling's approx.
from #temp

Note that you will have to make a case for 0!, if needed.