CODEWITHSUNDEEP
phpmysql
nfc
nfc

Reputation: 634

PHP MySQL select random rows

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 :)

Upvotes: 10

Views: 36496

Answers (6)

Jan Michaels
Jan Michaels

Reputation: 51

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.

Upvotes: 5

Marcus Adams
Marcus Adams

Reputation: 53880

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.

Upvotes: 0

nfc
nfc

Reputation: 634

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

Upvotes: 1

Dagg Nabbit
Dagg Nabbit

Reputation: 76786

change limit 1 to limit 6 on the eighth line.

Upvotes: 0

PIM
PIM

Reputation: 314

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
}

Upvotes: 0

OMG Ponies
OMG Ponies

Reputation: 332781

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.

Upvotes: 24

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