counting two columns

You have an audit table
       created       | action 
---------------------+--------
 2009-01-01 00:00:00 | create
 2009-01-02 00:00:00 | delete
 2009-01-15 00:00:00 | create
 2009-01-16 00:00:00 | create

and you want a report with two counts, created and deleted for each week

        week         | created | deleted 
---------------------+---------+---------
 2008-12-29 00:00:00 |       1 |       1
 2009-01-12 00:00:00 |       2 |       0


SELECT week, SUM(created) as created, SUM(deleted) as deleted
  FROM
  (
   (SELECT DATE_TRUNC('week', created_at) AS week, COUNT(*) as created, 0 as deleted
     FROM audits WHERE action = 'create' GROUP BY week)
  UNION
   (SELECT DATE_TRUNC('week', created_at) AS week, 0 as created, COUNT(*) as deleted
     FROM audits WHERE  action = 'delete' GROUP BY week)
  ) s
GROUP BY week
ORDER BY week ASC