PHP MySQL select random rows

Question

I have a problem selecting 6 random friends

This is the query I've got so far:

$result = num_rows("SELECT * FROM friends WHERE member_id = '".$_SESSION['userid']."'");
if($result >= 6) {
    $f_num = 6;
} else {
    $f_num = $result;
}
for($i = 1; $i <= $f_num; $i++) {
    $q_get_member_friends = mysql_query("SELECT * FROM friends WHERE member_id = '".$_SESSION['userid']."' ORDER BY rand() LIMIT 1");
    $r_get_member_friends = mysql_fetch_array($q_get_member_friends);
    echo $r_get_member_friends['friend_with'];
}

I want to select 6 random friends if the logged in user has more or equal to 6 friends

Stuck on this for a while now :/

Thanks for any help :)

Solution 1

If you use:

  SELECT * 
    FROM friends 
   WHERE member_id = '".$_SESSION['userid']."' 
ORDER BY rand() 
   LIMIT 6

If the person only has 3 friends, the query will only show those three - it doesn't mean that the query will always return six rows.

Solution 2

The best way I've found to select any number of random records is with OFFSET in the query.

Let's say you want 6 random records, so I'll borrow from an answer above and count the total number of friends in the database.

$sql = mysql_query("SELECT COUNT(*) AS total FROM friends WHERE member_id='". $_SESSION['userid'] ."'");

$get_count = mysql_fetch_array($sql); // Fetch the results

$numfriends = $get_count['total']; // We've gotten the total number

Now we'll get the 6 random records out of the total above (hopefully it's > 6),

$query = mysql_query("SELECT * FROM friends WHERE member_id='". $_SESSION['userid'] ."' LIMIT 6 OFFSET " . (rand(0, $numFriends));


while ($rows = mysql_fetch_array($query))
{
  /// show your $rows here
}

Using OFFSET may not be the best or most efficient, but it's worked for me on large databases without bogging them down.

Solution 3

Never mind, I figured it out :)
Had to use while not for :'D

Comments

[Endre Hovde]

do I have to use that query in a num_rows or fetch_array?

[cbednarski]

Order by rand is dangerously slow with lots of data.

[cbednarski]

There's an article here with details and alternatives: titov.net/2005/09/21/…