Convert multiple rows into one with comma as separator [duplicate]

Question

If I issue SELECT username FROM Users I get this result:

 username -------- Paul John Mary 

but what I really need is one row with all the values separated by comma, like this:

 Paul, John, Mary 

How do I do this?

Answer 1

 select    distinct       stuff((         select ',' + u.username         from users u         where u.username = username         order by u.username         for xml path('')     ),1,1,'') as userlist from users group by username 

had a typo before, the above works