I'm trying to select all members who have not registered for an event. I
have tables 'members', 'events', and 'events_members', the latter a join
table with event_id and member_id columns.
The closest I've gotten is with this query:
SELECT m.id, m.first_name, m.last_name
FROM members AS m
RIGHT JOIN events_members AS em ON
(em.event_id = 10 AND m.id != em.member_id)
ORDER BY m.last_name ASC;
This returns an empty set IF there are no records at all in
events_members with event_id = 10. But, in that case, I want to receive
ALL members.
However, if I add a single record with event_id = 10, I then get the
expected list of all OTHER members. How can I modify this query so that,
when there are 0 registered members for a particular event, I get back
all members?
Obviously, I could always first check for the existence of the event_id
in the join table and, if not found, run the select on the members
table. But I doubt that that's the best option.
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