[Boofo]

So your query should actually be:

PHP Code:

 $getusers = $db->query_read(" 
    SELECT user.username, userfield.field66 
    FROM " . TABLE_PREFIX . "user AS user
    LEFT JOIN " . TABLE_PREFIX . "userfield AS userfield ON user.userid=userfield.userid 
    WHERE userfield.field66 = '" . $variable . "' 
"); 


And ALWAYS use tablename AS tablename when you are accessing more than 1 table in a query.