PHP MySQL select random rows

Question

I have a problem selecting 6 random friends

This is the query I\'ve got so far:

$result = num_rows(\"SELECT * FROM friends WHERE member_id = \'\".$_S         


        

Answer 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.

Answer 2

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

Answer 3

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.

Answer 4

change limit 1 to limit 6 on the eighth line.

Answer 5

First select the number of friends that the user has:

"SELECT COUNT(*) as numFriends FROM friends WHERE member_id='".$_SESSION['userid']."'

...put that into a variable, let's call it "$numFriends" Then:

for($z=0;$z<6;$z++)
{
   $randomFriendIndex = rand(1,$numFriends);
   //Get the friend at that index
}

Answer 6

Instead of SELECT * at the beginning, try SELECT COUNT(*) and use the actual return value instead of num_rows().

Your loop could generate duplicates. I would suggest trying OMG Ponies answer.

There is a whole chapter about random selection in the book SQL Antipatterns.