From: "Michael Avila" <Michael.Avila.1@sbcglobal.net>
To: "SQL PostgreSQL MailList" <pgsql-sql@postgresql.org>
Subject: Re: Need SQL Help Finding Current Status of members
Date: Fri, 16 Dec 2005 08:46:03 -0500
Message-ID: <NBBBLNPHAMCFENDFHIDCIENFEGAA.Michael.Avila.1@sbcglobal.net>
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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)
>
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