Why is a UDF so much slower than a subquery?

Question

I have a case where I need to translate (lookup) several values from the same table. The first way I wrote it, was using subqueries:

SELECT
    (SELECT id FRO         


        

Answer 1

To get the same result (NULL if user is deleted or not active).

 select 
    u1.id as creator,
    u2.id as updater,
    u3.id as owner,
    [a.name]
 FROM asset a
        LEFT JOIN user u1 ON (u1.user_pk = a.created_by AND u1.active=1) 
        LEFT JOIN user u2 ON (u2.user_pk = a.created_by AND u2.active=1) 
        LEFT JOIN user u3 ON (u3.user_pk = a.created_by AND u3.active=1)