Question

Hello everyone I have been trying this for ages now.

I have read many questions here and tried adapting the varied solutions to my needs but without results.

History:

for an event there are many participants.
the participants all meet one another at the event and give out “likes” to all the other participants they actually like.

At the end of the event the admin inserts all the likes for each participant of THAT event, and the system will find the mutual likes (friendship)

Problem:
While inserting the likes i would like (pun) the system to detect weather a friendship is already established (from other events also) and if so avoid to display that user name when setting the likes.

Here are the tables that I’m using (mysql)

wp_fd_users

id | user_name | user_gender | .. etc

wp_fd_matches

id | event_id | event_user_id | event_user_match_id | … etc

Example of the match table

1 | 1 | 1 | 3 | ...
2 | 1 | 1 | 4 | ...
3 | 1 | 2 | 6 | ...
4 | 1 | 3 | 1 | ...

where you can clearly see that 1 <-> 3 have a mutual relationship and 1 likes 4 but not mutually.
I would need a query that returns all results that AVOID relationships that have been established in one single event.

An occurance like this:

1 | 1 | 1 | 3 | ...
2 | 1 | 1 | 4 | ...
3 | 1 | 2 | 6 | ...
4 | 2 | 3 | 1 | ...

would not trigger the like because it happens in two separate events

Hope it’s clear

Answer 1

YOur question is a little unclear. I am going by: “I would need a query that returns all results that AVOID relationships that have been established in one single event.”

The following self join accomplishes this:

select m1.*
from wp_fd_matches m1 left outer join
     wp_fd_matches m2
     on m1.event_id = m2.event_id and
        m1.event_user_id = m2.event_user_match_id
        m1.event_user_match_id = m2.event_user_id
where m2.id is null

It looks for the matching record. However, by using a left outer join, it is getting all records. It then filters out the ones with a match.