Message-ID: <43A29304.9050801@anpe.fr>
Date: Fri, 16 Dec 2005 11:12:20 +0100
From: Patrick JACQUOT <patrick.jacquot@anpe.fr>
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Cc: SQL PostgreSQL MailList <pgsql-sql@postgresql.org>
Subject: Re: Need SQL Help Finding Current Status of members
References: <NBBBLNPHAMCFENDFHIDCGENBEGAA.Michael.Avila.1@sbcglobal.net>
	<43A287C6.2090501@archonet.com>
In-Reply-To: <43A287C6.2090501@archonet.com>
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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)