Re: Need SQL Help Finding Current Status of members

On Fri, Dec 16, 2005 at 07:44:46PM -0500, Michael Avila wrote:
> Just tried it and it returned nothing.
>
> > > Select * from memberstatus A where not exists
> > > (select * from emberstatus B where B.member_id=A.member_id and
> > > B.status_date >A.status_date)
>
> Why the WHERE NOT EXISTS?

The query selects each row in memberstatus for which no other rows
(WHERE NOT EXISTS) with the same member_id have a later status_date;
in other words, the row(s) with the latest status_date for each
member_id. For example, given

member_id | status_code | status_date
-----------+-------------+-------------
1 | a | 2005-12-01
1 | b | 2005-12-02
1 | c | 2005-12-03
2 | x | 2005-12-11
2 | y | 2005-12-12
2 | z | 2005-12-13

the query should return

member_id | status_code | status_date
-----------+-------------+-------------
1 | c | 2005-12-03
2 | z | 2005-12-13

Offhand I can't think of why the query would return nothing unless
the table is empty, but maybe I'm overlooking something or making
unwarranted assumptions about the data. Can you post a sample data
set for which the query returns no rows?

--
Michael Fuhr