Question

I’ve got an official table, with id and name….

Officials may have supervisors – these are stored in a join table called officialsupervisor with official_id and supervisor_id as foreign keys to the official table.

I can show officials with their supervisor with

SELECT o.official_name Official, p.official_name Supervisor 
FROM officialsupervisor s, official o, official p 
WHERE o.official_id = s.official_id AND p.official_id = s.supervisor_official_id

I can list officials that don’t have a supervisor with

 SELECT o.official_name Official
 FROM  official o
 WHERE o.official_id NOT IN (SELECT official_id
 FROM officialsupervisor)

But I can’t work out how to list all officials with their supervisor, or a blank if they don’t have one. I feel as though this should be quite straightforward!

Thanks for any help.

Answer 1

Try this once:

SELECT o.official_name Official, p.official_name Supervisor
FROM official o
LEFT JOIN officialsupervisor s ON o.official_id = s.official_id
LEFT JOIN official p ON p.official_id = s.supervisor_official_id