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From: "David Johnston" <polobo@yahoo.com>
To: "'ssylla'" <stefansylla@gmx.de>, <pgsql-sql@postgresql.org>
References: <1328754679303-5468395.post@n5.nabble.com>
In-Reply-To: <1328754679303-5468395.post@n5.nabble.com>
Subject: Re: update column with multiple values
Date: Fri, 10 Feb 2012 11:08:11 -0500
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-----Original Message-----
From: pgsql-sql-owner@postgresql.org [mailto:pgsql-sql-owner@postgresql.org]
On Behalf Of ssylla
Sent: Wednesday, February 08, 2012 9:31 PM
To: pgsql-sql@postgresql.org
Subject: [SQL] update column with multiple values

Dear list,

sorry, I already posted this, but it did not seem to have been accepted by
the mailing list. So here's my second try:

I need to update all rows of a column ('parent') based on a subquery that
returns me the first four digits of another column ('id'):

UPDATE admin SET parent=(SELECT SUBSTR(id,1,4) FROM admin);


After executing, I get the following error-message:

"more than one row returned by a subquery used as an expressionmore than one
row returned by a subquery used as an expression"


I am not quite sure about that, but maybe I need to construct a
function/loop to fulfill this task?

thanks for help.

Stefan 

---------------------------------------------------------------

No sub-select required, just use the function:

UPDATE admin SET parent = substr(id,1,4);

This will, for each record, set the value of parent to the first four
characters of its ID.

When you use the sub-select there is not inherent linkage between the
"UPDATE" table and the "FROM" table.  You can make a correlated sub-query
but in this case the is necessary.

David J.