Following is an example to pull the list of user groups as found within security_users_vw:

( SELECT string_agg(su.security_users_name::text, ', '::text ORDER BY (su.security_users_name::text)) AS string_agg

           FROM security_groupings sg

             JOIN security_users su ON sg.group_id = su.security_users_id

          WHERE sg.user_id = u.security_users_id) AS "Groups"