Use count() instead of mysql_num_rows()

This guide explains why it is recommended to abandon the MySQL function mysql_num_rows() which simply returns the number of lines in a result.

The disadvantage of this function is that it is very heavy for the server since it is a loop that goes through each line to count them.

For example:

$SQLstr = "SELECT * FROM commentaires WHERE affiche=1";
$r = mysql_query($SQLstr);
$num = mysql_num_rows($r);

MySQL has a function count() that handles this and is much less resource-intensive. Use this:

$SQLstr = "SELECT count(*) FROM commentaires WHERE affiche=1"
$r = mysql_query($SQLstr);
$result = mysql_fetch_row($r);
$num = $result[0];

or

$SQLstr = "SELECT count(*) as total FROM commentaires WHERE affiche=1"
$r = mysql_query($SQLstr);
$result = mysql_fetch_array($r);
$num = $result['total'];