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

declare     @output varchar(max)

select      @output = coalesce
                      ( 
                          @output + ', ' + convert(varchar(max),cat_id), 
                          convert(varchar(max),cat_id)
                      )
from        yourTableHere

print       @output

Answer 2

And sometimes...

you have to answer your own question

declare     @output varchar(max)
select      @output = case when (@output is null) then '' else ', ' END + convert(varchar(max),cat_id)

Answer 3

check @output value just before the execution of this query, I think it's not equal to NULL but to '' (empty string)

EDIT: (after the @auth edited the question)

now I'm sure it's '',

you have to initialize it to NULL

to do it independently of CONCAT_NULL_YIELDS_NULL, use the old CASE WHEN:

select @output = NULL
select @output = CASE WHEN @output IS NULL THEN '' ELSE @output+', ' END + value