To: "A. Kretschmer" <andreas.kretschmer@schollglas.com>
Cc: <pgsql-sql@postgresql.org>
Subject: Re: Sql ORDER BY and ASC/DESC question
In-Reply-To: <20080130104226.GF26490@a-kretschmer.de> (A. Kretschmer's message
	of "Wed\, 30 Jan 2008 11\:42\:26 +0100")
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References: <aa457f86948348248e93c6fc38b4b1f6@pobox.sk>
	<20080130104226.GF26490@a-kretschmer.de>
From: Gregory Stark <stark@enterprisedb.com>
Organization: EnterpriseDB
Date: Wed, 30 Jan 2008 13:32:45 +0000
Message-ID: <87tzkvbfr6.fsf@oxford.xeocode.com>
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"A. Kretschmer" <andreas.kretschmer@schollglas.com> writes:

> am  Wed, dem 30.01.2008, um 11:35:51 +0100 mailte Jaroslav Sivy folgendes:
>> Hello everyone,
>> 
>> I have following problem: am using pl/sql functions to trigger some
>> sql code and i need to pass ORDER_BY column name and ASC/DESC sorting
>> order as an input parameters into that function and order the result
>> based on these input parameters.
>> 
>> The problem is, that the only way is to create query as "string" and
>> then execute it as "string".
>
> Right.
>> 
>> Is there any other way around how to avoid that "string query"?

If you're not concerned with the planner being able to find indexes to satisfy
these orderings (ie, you don't mind always doing a sort) you could do
something like:

ORDER BY 
 CASE ? 
 WHEN 1 THEN name ASC
 WHEN 2 THEN name DESC
 WHEN 3 THEN height ASC
 WHEN 4 THEN height DESC
 ELSE id ASC
 END

But to the planner this will be basically an opaque expression. It won't be
able to use any indexes on these columns. Also, incidentally you might want to
use text strings instead of integer labels.

-- 
  Gregory Stark
  EnterpriseDB          http://www.enterprisedb.com
  Get trained by Bruce Momjian - ask me about EnterpriseDB's PostgreSQL training!