SQL Query with joins and operators - php

Question

I'm having trouble with my most confusing query. It worked before but I must have changed a variable a couple of months ago, so now it doesn't work.
What it is meant to do is:
select * from users, * from media and * from friends
then allow the media to only be displayed if it contains a friends ID or you're own ID. However it its displaying the friends media but not my own. And the friends system is as follows: id, senders_id, recipient_id, status
Status being 0 (not accepted) and 1 (accepted)
Here is the following query:
SELECT DISTINCT users.id, users.firstname, users.lastname,
media.date, media.id, media.time, media.text, media.userID,
media.author_id, media.ip, media.post_id, media.format,
media.file_format, media.MediaTxt, media.author_firstname,
media.author_lastname, media.shared, media.relation
FROM users
JOIN friends
ON users.id IN (friends.sender, friends.recipient)
JOIN media
ON (users.id = media.userID)
WHERE 151 IN (friends.sender,friends.recipient)
AND media.relation = 'feed'
ORDER BY media.time DESC, media.date DESC
Primary and foreign keys:
friends.id (PRI Key)
media.id (PRI Key)
users.id (PRI Key)`
--
users.id is the same as media.UsrID and friends.recipient/sender

Answer 1

I think the big problem is that if a person has no friends (eg, user.id 151 above I'm guessing?) then the JOIN friends will result in zero rows returned.
You probably want to use LEFT JOINs, however there's bigger problems than that - the whole query is kind of hard to understand and perhaps not the best way to go about what you're after.
You're kind of saying "list each user and their friends along with all media they've uploaded. If user id 151 appears as either the sender or recipient in the friend relationship, give me the media." Even if you use left joins, that's not going to help friendless people, because those columns will be null. You need to also add in the so.users_id to the compare list, eg:
SELECT DISTINCT users.id, users.firstname, users.lastname,
media.date, media.id, media.time, media.text, media.userID,
media.author_id, media.ip, media.post_id, media.format,
media.file_format, media.MediaTxt, media.author_firstname,
media.author_lastname, media.shared, media.relation
FROM users
LEFT JOIN friends
ON users.id IN (friends.sender, friends.recipient)
JOIN media
ON (users.id = media.userID)
WHERE 151 IN (users.id, friends.sender,friends.recipient)
AND media.relation = 'feed'
ORDER BY media.time DESC, media.date DESC
Note, I didn't bother LEFT JOINing media, since it's media you're after and returning blanks is kind of pointless.
The query is still written a little backwards though - it might be clearer if you wrote it something like:
SELECT DISTINCT users.id, users.firstname, users.lastname,
media.date, media.id, media.time, media.text, media.userID,
media.author_id, media.ip, media.post_id, media.format,
media.file_format, media.MediaTxt, media.author_firstname,
media.author_lastname, media.shared, media.relation
FROM users
JOIN media
ON (users.id = media.userID)
LEFT JOIN friends
ON users.id IN (friends.sender, friends.recipient)
WHERE 151 IN (users.id, friends.sender, friends.recipient)
AND media.relation = 'feed'
ORDER BY media.time DESC, media.date DESC
Also, I sure hope 151 is replaced with a positional parameter, so you don't introduce SQL injection attacks!