From: Tom Lane <tgl@sss.pgh.pa.us>
To: Erik Thiele <erik@thiele-hydraulik.de>
Cc: pgsql-sql@postgresql.org
Subject: Re: summing tables
Date: Tue, 15 Jul 2003 11:14:56 -0400
Message-ID: <22671.1058282096@sss.pgh.pa.us> (raw)
In-Reply-To: <20030715143925.54716ed4.erik@thiele-hydraulik.de>
References: <20030715140921.7c5a6a6c.erik@thiele-hydraulik.de>
<001501c34aca$e70ca280$0600a8c0@fix.ro>
<20030715143925.54716ed4.erik@thiele-hydraulik.de>
Erik Thiele <erik@thiele-hydraulik.de> writes:
> "Viorel Dragomir" <bigchief@vio.ro> wrote:
>> update table_name
>> set c = a + b + (select c from table_name as x where x.seq = seq-1)
>> where c is null;
> hmmm. the query is run row by row, isn't it?
> but it will have different results depending on the order of those rows.
No, it won't, because the SELECTs will not see the changes from the
not-yet-completed UPDATE. The above command is almost right; it needs
to be
update table_name
set c = a + b + (select c from table_name as x where seq = table_name.seq-1)
where c is null;
because inside the sub-SELECT, unadorned "seq" will refer to the SELECT's
table.
You didn't say exactly what you wanted to do with null inputs, so that
issue may need more thought.
regards, tom lane
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To: pgsql-sql@postgresql.org
Cc: tgl@sss.pgh.pa.us, erik@thiele-hydraulik.de
Subject: Re: summing tables
In-Reply-To: <22671.1058282096@sss.pgh.pa.us>
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