Question

• I have a feature to search for users on my website,
• I also have a feature for friends on my site.
• I have a query to search for the correct users on my site, and
• I have a query that determines the users that a user is friends with, they both work as they should,

so what i need assistance with is combining the two, to order friends before other users.

Search query:

SELECT userID, fname, lname, 
FROM names 
WHERE (
    fname LIKE '".$term."%' 
    OR lname LIKE '".$term."%' 
    OR CONCAT(fname, ' ', lname) LIKE '".$term."%'
      ) 
AND userID!=$session 
ORDER BY fname ASC, lname ASC 
LIMIT 10

Friends query:

SELECT CASE WHEN userID=$session 
            THEN userID2 
            ELSE userID 
            END AS friendID 
FROM friends
WHERE (
       userID=$session 
       OR userID2=$session
       ) 
AND state='1'

so, a statement that would compare the two should be something like, IF names.userID=friends.friendID

Now I found a users suggestion for a similar issue on stackoverflow that seems like it would be a simple way of doing this, however I’m not entirely sure how to add it with my particular friends query, as it’s more of a complex query.

SELECT
    posting.id,
    IF(a.friend_id = b.criteria, 1, 0) AS is_friend
...
ORDER BY is_friend DESC, posting.id DESC

Answer 1

Use an outer join (left join) to join the user list returned by your first query with the friend list that your second query produces. Now you’ll be able to sort on the fact whether the second row set has a match: if it does, the corresponding row should go first.

This is an example of how you could implement the above:

SELECT
  n.userID,
  n.fname,
  n.lname
FROM names n
LEFT JOIN (
  SELECT CASE WHEN userID=$session 
              THEN userID2 
              ELSE userID 
              END AS friendID 
  FROM friends
  WHERE (
         userID=$session 
         OR userID2=$session
         ) 
  AND state='1'
) f
ON n.userID = f.friendID
WHERE (
    n.fname LIKE '".$term."%' 
    OR n.lname LIKE '".$term."%' 
    OR CONCAT(n.fname, ' ', n.lname) LIKE '".$term."%'
      ) 
AND n.userID!=$session 
ORDER BY (f.friendID IS NULL), n.fname ASC, n.lname ASC 
LIMIT 10

The first sorting criterion, (f.friendID IS NULL), evaluates to false if there’s a matching f row, i.e. if the user is a friend, and to true otherwise. Consequently, since false sorts before true, the friends will be sorted before non-friends.