something like this
select * from user u,trade t, trade_photo tp where u.user_id=t.user_id and t.trade_id=tp.trade_id;
if you want to select for a particular user
select * from user u,trade t, trade_photo tp where u.user_id=some_id and u.user_id=t.user_id and t.trade_id=tp.trade_id;