Clear Cache

This is supposed to clear the cache but as usual I can't work Drupal out.

Even though the logs are set to clear anything older than 2 weeks, you have to run cron.php to clear the logs, mad!

<?
echo "This page runs a script that clears the main cache.<br>";
$sql = "DELETE from cache WHERE 1";
$result = mysql_query($sql);
echo "It's clear now.<br>";
?>