From: | Scott Marlowe <smarlowe(at)g2switchworks(dot)com> |
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To: | Hector Rosas <jeziel(dot)rosas(at)gmail(dot)com> |
Cc: | pgsql-sql(at)postgresql(dot)org |
Subject: | Re: Selecting records not present in related tables |
Date: | 2005-10-06 20:13:41 |
Message-ID: | 1128629621.29347.242.camel@state.g2switchworks.com |
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Thread: | |
Lists: | pgsql-sql |
On Thu, 2005-10-06 at 14:43, Hector Rosas wrote:
> Hello, I'm trying to select records in a table not present in a
> related table, in example, I've a table with message information
> (subject, message, date, etc) and another (usermessages) with where
> user(s) has that message, its state, etc. Records in this table will
> be deleted in a certain time (just some extra info).
> I want to select messages records that aren't present in the other
> table (usermessages), I got the next two queries, maybe someone can
> suggest a better one.
A fairly common way to do this is to use a left join and a not null:
select a.id from tablea a left join tableb b on (a.id=b._aid) where
b._aid IS NULL
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