T-SQL scalar function to generate pseudonymised character IDs from integer IDs

id2alpha.sql

-- The function is used to convert employee ID into a (random) 
-- character. To achieve randomness a seed should be generated by a caller.
-- Note: the number of IDs to be encoded cannot be greater than 62, otherwise
--		the function will return conflicting characters. To increase the number of handled
--		IDs extended the @chars variable
-- Usage:
--		select dbo.fn_id2alpha(1223, 42, 


create function [dbo].[fn_id2alpha](@id int, @seed int, @n int)  
-- @id - ID to be converted into a random char
-- @seed - random number, use select @seed = floor(rand()*100) to init
-- @n - the total number of IDs to be randomly encoded, should be no greater than 62
returns nvarchar(1)
as
begin
	declare @chars nvarchar(255)
	select @chars = 'ABCDEFGHIJKLMNOPQRSTUVWXYZabcdefghijklmnopqrstuvwxyz0123456789'
	if @n > len(@chars) select @n = len(@chars)
	select @id = (@id + @seed)%@n + 1
	return substring(@chars, @id, 1) 
end