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Select only active entries

From: "Carel Combrink" <s25291930(at)tuks(dot)co(dot)za>
To: "PostgreSQL Novice List" <pgsql-novice(at)postgresql(dot)org>
Subject: Select only active entries
Date: 2010-07-20 13:44:46
Message-ID: (view raw, whole thread or download thread mbox)
Lists: pgsql-novice

I have a table that looks as follow:

=# SELECT id, is_active FROM test_select;
  id | is_active
   5 | t
   5 | f
   6 | t
   7 | t
   8 | t
   5 | t
   8 | f
   9 | t
  10 | t
   6 | f
  10 | f
(11 rows)

I want to create a query to select only the latest ones that are  
active, is there an easy way to do this or should I rethink my design?  
The table will not be very big? (I am very new to PostgreSQL and  
select queries)

I want the following result from a select query:
=#SELECT id, is_active FROM test_select WHERE <where conditions>;
  id | is_active
   5 | t
   7 | t
   9 | t
(3 rows)

I cant assume that those with uneven number of entries are active  
since one can have the situation where one sets it active and then  
sets it active again and then deactivates it. Or should I rather make  
sure this does not happen and then return all the entries with an  
uneven number of entries? How would such a query look to return the  
uneven entries?

I cant use update since I want to retain the history of what happened when.

Any help will be appreciated.
Using: PostgreSQL 8.4 on Ubuntu 10.04

Carel Combrink

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Subject: Re: Select only active entries
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