Building a comma separated list?

Question

I\'m tryin to use SQL to build a comma separated list of cat_id\'s

the code is:

declare     @output varchar(max)
set         @output = null;
select @         


        

Answer 1

COALESCE Returns the first nonnull expression among its arguments

First argument @output + ', ' is never null (unless you initialize @output as null AND set CONCAT_NULL_YIELDS_NULL to ON), so it's always returned.