Need SQL guru for a complex query - mysql

Question

I have several tables that I am trying to get some data out of, and I am very close, but cannot quite close the deal.
I have the following tables:
EVENT
USER
FRIEND
USER__FRIEND
EVENT__INVITATION
USER and FRIEND are linked via the USER__FRIEND table (which contains a USER_ID and a FRIEND_ID field)
EVENT__INVITATION links an EVENT with a FRIEND (it has EVENT_ID and INVITEE_ID)
I am trying to get all EVENTS where:
I am the EVENT creator ($myUserID = EVENT.CREATOR_ID)
or I am invited to the event ($myUserID = EVENT__INVITATION.INVITEE_ID)
or one of my FRIENDs is the creator of the EVENT ($myUserID = USER__FRIEND.USER_ID AND EVENT.CREATOR_ID IN (list of my FRIENDs))
or one of my FRIENDs is invited to the EVENT ($myUserID = USER__FRIEND.USER_ID AND EVENT__INVITATION.INVITEE_ID IN (list of my FRIENDs))
There are some other WHERE conditions around other parameters, but I think I can sort those out on my own.
Right now the only way I could get this to work was with a UNION, which I think must be a cop-out, and if I had better chops I could get around using it.
So, the question is, can this be done with a single, inexpensive query that does not use a UNION?
Here is what I have so far, which accomplishes everything except the EVENTs that my FRIENDs are invited to (23 is the passed in userID in this case):
SELECT e.*
FROM event e
LEFT JOIN event__invitation ei ON ei.event_id = e.id
LEFT JOIN user__friend uf ON uf.friend_id = ei.invitee_id
LEFT JOIN friend f ON f.id = uf.friend_id
WHERE (ei.invitee_id = 23 OR e.creator_id = 23 OR uf.user_id = 23 OR f.user_id = e.creator_id)
AND e.start_time >= 1348000000
and this is the query with the UNION:
SELECT e.* FROM event e
INNER JOIN event__invitation ei ON ei.event_id = e.id
INNER JOIN user__friend uf ON uf.friend_id = ei.invitee_id
WHERE (e.creator_id = 23 OR ei.invitee_id = 23 OR uf.user_id = 23)
UNION
SELECT e1.* FROM event e1
WHERE e1.creator_id IN (
SELECT f1.user_id FROM friend f1
INNER JOIN user__friend uf1 ON uf1.friend_id = f1.id
WHERE uf1.user_id = 23
AND f1.user_id IS NOT NULL
);
There is more to the query that makes the use of the UNION undesireable. I have a complex trig calculation that I am doing in the main select, and am ordering the results by that value. I think may mess up the result set.
Thanks for any help!!

Answer 1

How about the following:
-- take only distinct events
SELECT DISTINCT e.*
-- start with the event
FROM event e
-- expand to include all invitees and their user_friend info
LEFT JOIN event__invitation ei
ON ei.event_id = e.id
LEFT JOIN user__friend invitee
ON invitee.friend_id = ei.invitee_id
-- now we join again to user_friend to get the friends of the invitees/the creator
LEFT JOIN user__friend invitedFriend
ON invitedFriend.user_id = invitee.user_id
OR invitedFriend.user_id = e.creator_id
-- finally we match on whether any of these friends of friends are myself
LEFT JOIN friend myselfAsAFriend
ON myselfAsAFriend.id = invitedFriend.friendId
AND myselfAsAFriend.userID = 23
WHERE
(
-- (1) I am the creator of the event
e.creator_id = 23
-- (2) I am invited to the event
OR invitee.user_id = 23
-- (3 and 4) for this join to match a friend of mine must be invited or the creator
OR myselfAsAFriend.id IS NOT NULL
)
AND e.start_time >= 1348000000

Answer 2

I'm not very good at query tuning presently, so I would just give something like this a try and let the optimiser to put its effort in figuring out the best way of getting the results:
SELECT DISTINCT e.*
FROM event e
INNER JOIN event__invitation ei ON ei.event_id = e.id
INNER JOIN (
SELECT friend_id
FROM user__friend
WHERE user_id = $myUserID
UNION ALL
SELECT $myUserID
) u ON u.friend_id IN (e.creator_id, ei.invitee_id)
;
If this doesn't prove efficient enough, you could always go with something like #ChaseMedallion's suggestion, as it may indeed turn out a better one for your case.