Using ORDER BY on a multiple LEFT JOIN query - mysql

Question

I have this long query that I finally got to work but I am unable to ORDER BY date_time_added, which is a field that is in all the tables except for user_accounts and relationships table. How do i make it work correctly?
$sql = "select distinct pb.user_id, pb.Full_name,
tv.why_onsite3, tv.onsite3_id, tv.other_date as onsite3_date,
tv.user_allowed as tv_user_allowed, np.onsite4_name ,
np.onsite4_id, np.other_date as onsite4_date, np.user_allowed
as np_user_allowed, pml.med_name , pml.med_id, pml.other_date
as pml_date, pml.user_allowed as pml_user_allowed, pl.onsite5_name,
pl.onsite5_test_id, pl.other_date as some_stats_date, pl.user_allowed as
pl_user_allowed, chlp.problem_name_is , chlp.current_problem_id,
chlp.other_date as chlp_date, chlp.user_allowed as chlp_user_allowed,
pphl.onsite10_health_prob_id , pphl.onsite10_problem_name_is,
pphl.other_date as pphl_date, pphl.user_allowed as pphl_user_allowed,
al.onsite_id , al.onsite_name, al.other_date as onsite_date,
al.user_allowed as al_user_allowed, sl.onsite2_id , sl.onsite2_name,
sl.other_date as onsite2_date, sl.user_allowed as sl_user_allowed,
hal.onsite6_id , hal.reason_for_admit, hal.other_date as hal_date,
hal.user_allowed as hal_user_allowed, il.onsite9_id , il.onsite9_name,
il.other_date as il_date , il.user_allowed as il_user_allowed
from user_accounts pb left join some_stuff tv on pb.user_id = tv.user_id
left join some_onsite4s np on pb.user_id = np.user_id
left join some_med pml on pb.user_id = pml.user_id
left join list_hal hal on pb.user_id = hal.user_id
left join list_for_things il on pb.user_id = il.user_id
left join list_on sl on pb.user_id = sl.user_id
left join some_all al on pb.user_id = al.user_id
left join some_list pphl on pb.user_id = pphl.user_id
left join some_stats pl on pb.user_id = pl.user_id
left join some_probs chlp on pb.user_id = chlp.user_id
where (pb.user_id in (select fb.friend_id from relationships fb
where fb.user_id = '$uid')
or pb.user_id in (select fb1.user_id from relationships fb1
where fb1.friend_id = '$uid')
)
group by pb.user_id ORDER BY date_time_added DESC LIMIT $startrow, 20";

Answer 1

In ORDER BY clause, you have to specify what is the exact column you are ordering by. That means you have to prefix the column that is used for ordering, because you have multiple columns that are called the same in multiple tables.
Other option is to restructure the query completely and use UNION operator with multiple SELECT statements. Each SELECT statement would pickup a group of data from one table and order that group by column from that table.
The solution depend on the data that you want to output - the context of the data.