Question

What I ended up doing was taking two SQL queries and using the array_intersect() in PHP to filter out the results:

$sql1 = 'SELECT z.*, u.username, u.user_colour, u.username_clean, u.user_avatar, u.user_avatar_type
    FROM ' . ZEBRA_TABLE . ' z, ' . USERS_TABLE . ' u
    WHERE (( z.user_id = ' . $user->data['user_id'] . '
        AND z.friend = 1
        AND u.user_id = z.zebra_id )
            OR ( z.zebra_id = ' . $user->data['user_id'] . '
                AND z.friend = 1
                AND u.user_id = z.user_id ))
    ORDER BY u.username_clean ASC';

$sql2 = 'SELECT z.*, u.username, u.user_colour, u.username_clean, u.user_avatar, u.user_avatar_type
    FROM ' . ZEBRA_TABLE . ' z, ' . USERS_TABLE . ' u
    WHERE (( z.user_id = ' . $user_id . '
        AND z.friend = 1
        AND u.user_id = z.zebra_id )
            OR ( z.zebra_id = ' . $user_id . '
                AND z.friend = 1
                AND u.user_id = z.user_id ))
    ORDER BY u.username_clean ASC';

The structure of both queries are the same and the only difference is $user->data['user_id] (first person) is replaced with $user_id (second person) in the second query. I want to retrieve friends that both users have in common. Could anyone merge this into a single query so that I don’t have to use two queries and call array_intersect()?

Answer 1

Well, you could always just subquery both:

$sql = 'SELECT a.* 
    FROM ('.$sql1.') AS a 
    JOIN ('.$sql2.') AS b ON a.user_id = b.user_id AND a.username = b.username';

You may want to add u.user_id to the field list of both queries u.user_id AS u_user_id then change the second join clause from a.username = b.username to a.u_user_id = b.u_user_id…

EDIT: Now that I really look at it closer, those two queries are almost identical… Why not just do something like this (replace the where clause to this):

WHERE z.friend = 1 
   AND (
       ( z.user_id = '.$user_id.' AND u.user_id = z.zebra_id )
        OR
       (z.zebra_id = '.$user_id.' AND u.user_id = z.user_id )
   ) AND (
       ( z.user_id = '.$user->data['user_id'].' AND u.user_id = z.zebra_id )
        OR
       (z.zebra_id = '.$user->data['user_id'].' AND u.user_id = z.user_id )
   ) 

That should give you the result of both queries intersected, and be faster since it can optimize better (hopefully)…

Oh, and they are in different where blocks because there’s a few cases where z.user_id matches $user_id, but z.zebra_id matches $user->data['user_id']… So rather than list all the permutations, I just layed it out like this…