Re: Need SQL Help Finding Current Status of members - Mailing list pgsql-sql

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?

Here is a copy and paste of my code

$query = "SELECT * FROM memberstatus A WHERE NOT EXISTS (SELECT * from
memberstatus B WHERE B.member_id=A.member_id AND B.status_date >
A.status_date)";

Mike


> -----Original Message-----
> From: Michael Avila [mailto:Michael.Avila.1@sbcglobal.net]
> Sent: Friday, December 16, 2005 8:46 AM
> To: SQL PostgreSQL MailList
> Subject: RE: [SQL] Need SQL Help Finding Current Status of members
>
>
> Interesting. I think I understand that. I have never worked with
> a SELECT within a SELECT (I think that is called a subquery). I
> am guessing that it works its way through the member status
> records until the latest date "floats" to the top (nothing is > than it).
>
> Will that be a problem performance-wise if there are thousands of records?
>
> Thanks for the help.
>
> Mike
>
>
> > -----Original Message-----
> > From: pgsql-sql-owner@postgresql.org
> > [mailto:pgsql-sql-owner@postgresql.org]On Behalf Of Patrick JACQUOT
> > Sent: Friday, December 16, 2005 5:12 AM
> > Cc: SQL PostgreSQL MailList
> > Subject: Re: [SQL] Need SQL Help Finding Current Status of members
> >
> >
> > Richard Huxton wrote:
> >
> > > Michael Avila wrote:
> > >
> > >> I have a table which keeps track of the status of members. In the
> > >> table is
> > >>
> > >> member_id int(8)
> > >> status_code char(1)
> > >> status_date date
> > >> KEY member_id (member_id,status_code,status_date)
> > >>
> > >>
> > >> Each member can have multiple records because a record is added each
> > >> time
> > >> the status changes but the old record is kept for history.
> > >>
> > >> What I want to do is find the latest status for each member.
> > >
> > >
> > > Michael Fuhr has already described on solution, but if you can alter
> > > the table definition then there might be a neater solution.
> > >
> > > Replace "status_date" with "status_expires" and make it a "timestamp
> > > with time zone". Set the expiry to 'infinity' for the current record
> > > and  you then have a simple select to find the most recent.
> > >
> > > If you regularly want to find which record was active on a particular
> > > time you'll want two columns: valid_from and valid_to. This makes it
> > > much easier to find a row for a specific date.
> >
> > There is a standard way :
> >
> > 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)
> >
> > ---------------------------(end of broadcast)---------------------------
> > TIP 5: don't forget to increase your free space map settings