Received: from verde.onda.com.br (verde.onda.com.br [200.195.192.10])
	by mail.postgresql.org (8.11.1/8.11.1) with ESMTP id eA5LfCs68202
	for <pgsql-sql@postgresql.org>; Sun, 5 Nov 2000 16:41:13 -0500 (EST)
	(envelope-from cdallacosta@bigfoot.com)
Received: from terrificus (cmcta002p161.onda.com.br [200.195.205.161])
	by verde.onda.com.br (8.8.8/8.8.8) with SMTP id TAA20882
	for <pgsql-sql@postgresql.org>; Sun, 5 Nov 2000 19:41:00 -0200 (EDT)
Message-ID: <003f01c0477a$04717320$02ffa8c0@terrificus>
From: "=?iso-8859-1?Q?Crist=F3v=E3o_B._B._Dalla_Costa?="
	<cdallacosta@bigfoot.com>
To: "pgsql-sql" <pgsql-sql@postgresql.org>
References: <Pine.SGI.3.96.1001106015029.1002323A-100000@www.cdfd.org.in>
Subject: Re: Conditional SQL query
Date: Sun, 5 Nov 2000 19:44:53 -0300
MIME-Version: 1.0
Content-Type: text/plain;
	charset="iso-8859-1"
Content-Transfer-Encoding: 7bit
X-Priority: 3
X-MSMail-Priority: Normal
X-Mailer: Microsoft Outlook Express 5.50.4133.2400
X-MimeOLE: Produced By Microsoft MimeOLE V5.50.4133.2400
X-Archive-Number: 200011/37
X-Sequence-Number: 68

>
> Now I have one more problem. How do I insert only once if value does not
> exist? eg:
>

You should create a unique index on the appropriate fields. For example:

CREATE UNIQUE INDEX indexname ON table (field1, field2)

Then the insert will fail if this particular combination of the values of
(field1, field2) is already in the table.

Be careful if the insert is inside a transaction, tough. If it fails due to
non-uniqueness your transaction will be aborted (all further queries ignored
untill a COMMIT or ROLLBACK).