MYSQL: Getting certain data from a cross join depending on condition -

this problem query:

select distinct        t.name tname,        t.task_group tg,       tgs.name tgname       tasks t, task_users tu, task_groups tgs       (tu.worker = 1 , t.keyid = tu.task , tgs.keyid = t.task_group); 

the query works. thing part of clause tgs.keyid = t.task_group filters out results condition not true (which is, of course correct).

how can modify query , still tname when condition not true , in case obtain predefined string tgname?

to give information when condition not true t.task_group allways -1. in case tgname of "n/a".

how can this?

use case...when...else...end:

select distinct        t.name tname,        t.task_group tg,       case when tgs.keyid = t.task_group tgs.name else 'something else' end tgname       tasks t, task_users tu, task_groups tgs       (tu.worker = 1 , t.keyid = tu.task);