Question

This is for the friends module on my site, where users can make friends with each other.
These are stored in a “friends:” table, with person who initiated the friendship being the friendship_inviter and the person on the approve/deny end of things is the friendhsip_accepter

SELECT user_id, user_name, user_gender
FROM friends
LEFT JOIN users
    ON (   users.user_id = friends.friendship_inviter 
        OR users.user_id = friends.friendship_accepter)
WHERE (friendship_inviter = '125' OR friendship_accepter = '125') 
AND    user_id !='125' 
AND    friendship_level = 1;

This does a full table scan, and even though the tables are not large (15,000 users, 3000 friendships), it takes 1-1.5 seconds on average.

How can I output this list of current friends in a way that would be less taxing n the server?

Answer 1

SELECT user_id, user_name, user_gender
FROM friends
LEFT JOIN users
    ON users.user_id = friends.friendship_accepter
WHERE  friendship_accepter = '125' 
AND    user_id !='125' 
AND    friendship_level = 1
UNION 
SELECT user_id, user_name, user_gender
FROM friends
LEFT JOIN users
    ON users.user_id = friends.friendship_inviter
WHERE friendship_inviter = '125'  
AND    user_id !='125' 
AND    friendship_level = 1;

Of course, it looks like you aren’t selecting anything from the “friends” table, AND you have extra columns in your WHERE clause, so I would actually write INNER JOINs instead, which are equivalent to the LEFT JOINs in the case you posted:

SELECT user_id, user_name, user_gender
FROM friends
INNER JOIN users
    ON users.user_id = friends.friendship_accepter
WHERE  friendship_accepter = '125' 
AND    user_id !='125' 
AND    friendship_level = 1
UNION 
SELECT user_id, user_name, user_gender
FROM friends
INNER JOIN users
    ON users.user_id = friends.friendship_inviter
WHERE friendship_inviter = '125'  
AND    user_id !='125' 
AND    friendship_level = 1;