哪个更有效率？ mysql subselect还是php switch？ [关闭]

Question

OK, so, there are two ways in which I can achieve the same result, a Subselect in my query as follows:

SELECT nu.id, nu.username, nu.user_level, nu.phpbb_id, nu.real_name, nu.telephone, nu.email, nu.monster_points, nu.ref_points, 
(SELECT lv.name FROM hh_user_levels lv WHERE lv.user_level = nu.user_level) AS 'level_name' FROM hh_user_new nu

OR by using a PHP switch on a statement without the subselect as follows:

switch($result['user_level'])   {
    case 0:
        $level_name = 'Not Logged In';
        break;
    case 1:
        $level_name = 'basic user';
        break;
    case 2:
        $level_name = 'member';
        break;
}

(there are actually 10 possibilities, but I didn't think you'd be interested in all of them!)

So, my question is, which is more efficient? Achieving this through a MySQL subselect or via the PHP switch on each result?

Cheers!

Seb

Answer 1

Subselects are notoriously performances killer... so, i'd say PHP. Even if, probably, for practical reasons i'd go for a MySQL query with a regular JOIN...