$query = "select ID, FileName from files";
$result = mysql_query($query) or die("Query failed : " . mysql_error());
while($row = mysql_fetch_array($result, MYSQL_NUM))
{
$arr[$row[0]] = $row[1];
}
$query = "select count(*) as cnt,FileID from `files_downloaded` where *условие_для_даты* group by FileID order by cnt desc
limit 0,100";
$result = mysql_query($query) or die("Query failed : " . mysql_error());
while($row = mysql_fetch_array($result, MYSQL_NUM))
{
echo "File ".$arr[$row[1]]." was downloaded ".$row[0]." times";
}