To: Kaloyan Iliev Iliev <news1@faith.digsys.bg>
Cc: pgsql-sql@postgresql.org
Subject: Re: Problems with UNION ALL and ORDER BY 
In-reply-to: <410E6E42.6030206@faith.digsys.bg> 
References: <410E6376.1010404@faith.digsys.bg>
 <10984.1091464511@sss.pgh.pa.us>
	<410E6E42.6030206@faith.digsys.bg>
Comments: In-reply-to Kaloyan Iliev Iliev <news1@faith.digsys.bg>
	message dated "Mon, 02 Aug 2004 19:39:30 +0300"
Date: Mon, 02 Aug 2004 13:09:42 -0400
Message-ID: <12126.1091466582@sss.pgh.pa.us>
From: Tom Lane <tgl@sss.pgh.pa.us>

Kaloyan Iliev Iliev <news1@faith.digsys.bg> writes:
> As I say in my previous letter I am using 7.2.3. If you wish I can show 
> you the query and the result to see for yourself, that there is 
> something wrong. It just don't order the overall result but the separate 
> results of the both subqueries.

Quite honestly, I don't believe it.  In 7.2 I get

regression=# explain select * from tenk1 a union all select * from tenk1 b order by unique1;
NOTICE:  QUERY PLAN:

Sort  (cost=3128.28..3128.28 rows=20000 width=148)
  ->  Append  (cost=0.00..760.00 rows=20000 width=148)
        ->  Subquery Scan *SELECT* 1  (cost=0.00..380.00 rows=10000 width=148)
              ->  Seq Scan on tenk1 a  (cost=0.00..380.00 rows=10000 width=148)
        ->  Subquery Scan *SELECT* 2  (cost=0.00..380.00 rows=10000 width=148)
              ->  Seq Scan on tenk1 b  (cost=0.00..380.00 rows=10000 width=148)

EXPLAIN

and as you can see there's only one sort step being applied to the union
result.

Now if EXPLAIN shows you a different sorting structure for your query,
then I'd be interested to see the exact query and the EXPLAIN output.
But what I think is that you are misinterpreting the sorting result you
get.  If you are using a non-C locale you may be seeing some pretty
weird sorting rules :-(

			regards, tom lane