note 71153 added to function.rand

The problem with these random row functions below is that they require you to fetch all the query results first. Now this may be OK for a small resultset - but in that case why not just use the SQL 'ORDER BY RAND() LIMIT 10' to do the job. The real problem arises when you want a small random selection from a large query resultset; in that case the SQL RAND() function causes the query to run very slowly. It is then that we need to do the processing in php, and fetching every row from a large query resultset first rather defeats the purpose. The following is a far simpler and more efficient solution to this problem. It will also cope with queries that do not return distinct rows. <?php function randomselection($c, $sql) { // run the query $result=mysql_query($sql) or die($sql); // get the upper limit for rand() $up = mysql_num_rows($result)-1; // check that there is more data than rows required if ($up <= $c) { while ($row=mysql_fetch_assoc($result)) { $selection[] = $row; } return $selection; } // set up array to hold primary keys and elliminate duplicates // since random DOES NOT mean unique // or the query may not return DISTINCT rows $keys = array(); // get random selection while (count($keys) < $c) { // get random number for index $i = rand(0, $up); // move pointer to that row number and fetch the data mysql_data_seek($result, $i); $row = mysql_fetch_assoc($result); // check if the primary key has already been fetched if (!in_array($row['id'], $keys)) { // store the row $selection[] = $row; // store the id to prevent duplication $keys[] = $row['id']; } } return $selection; } ?> Fully tested and certified bug-free ;) ---- Server IP: 83.138.144.80 Probable Submitter: 213.120.98.128 ---- Manual Page -- http://www.php.net/manual/en/function.rand.php Edit -- https://master.php.net/note/edit/71153 Del: integrated -- https://master.php.net/note/delete/71153/integrated Del: useless -- https://master.php.net/note/delete/71153/useless Del: bad code -- https://master.php.net/note/delete/71153/bad+code Del: spam -- https://master.php.net/note/delete/71153/spam Del: non-english -- https://master.php.net/note/delete/71153/non-english Del: in docs -- https://master.php.net/note/delete/71153/in+docs Del: other reasons-- https://master.php.net/note/delete/71153 Reject -- https://master.php.net/note/reject/71153 Search -- https://master.php.net/manage/user-notes.php