[RESOLVED] How to add WHERE condition to GROUP BY

[cretaceous]

SELECT mailer_subjectline, pdf_placename, pdf_newslet_cat, 
trackpg_url, track_hits, mailer_tdate, mlr.mailer_id , SUM(track_hits) as tothits 
FROM mass_mailer AS mlr 
LEFT JOIN pdfs as p ON (mlr.pdf_id =p.pdf_id)
LEFT JOIN mail_track AS trk ON (mlr.mailer_id=trk.mailer_id ) 
LEFT JOIN mail_track_pages AS pgs ON (trk.trackpg_id=pgs.trackpg_id )
 GROUP BY trk.trackpg_id 
ORDER BY mlr.mailer_tdate DESC, pgs.trackpg_id 

Can anyone help on above query ...
The problem is on "SUM(track_hits) as tothits " with "group by trk.trackpg_id "

But that is summing all the track_hits - I need to split them by the mailer id

What I want it to do is something like:
GROUP BY trk.trackpg_id WHERE mlr.mailer_id=trk.mailer_id

any tips?

[cretaceous]

aha:
GROUP BY trk.trackpg_id, trk.mailer_id