Re: Selecting rows with "static" ordering

["Phillip Smith" <phillip(dot)smith(at)weatherbeeta(dot)com(dot)au>]

The best I can think of off the top of my head would still be multiple SQL,
but at least it would be in one transaction block:

BEGIN;
SELECT '1' AS ordering, t1.* INTO TEMP TABLE work_table FROM t1 WHERE t1.id
= '3';
SELECT '2' AS ordering, t1.* INTO TEMP TABLE work_table FROM t1 WHERE t1.id
= '2';
SELECT '3' AS ordering, t1.* INTO TEMP TABLE work_table FROM t1 WHERE t1.id
= '5';
SELECT '4' AS ordering, t1.* INTO TEMP TABLE work_table FROM t1 WHERE t1.id
= '1';
SELECT '5' AS ordering, t1.* INTO TEMP TABLE work_table FROM t1 WHERE t1.id
= '4';
SELECT t1.* FROM work_table ORDER BY ordering;
COMMIT;

Something to that effect...? It's at least makes it only 1 connection from
the client to the database.


-----Original Message-----
From: pgsql-sql-owner(at)postgresql(dot)org [mailto:pgsql-sql-owner(at)postgresql(dot)org]
On Behalf Of Steve Midgley
Sent: Friday, 27 April 2007 10:01
To: pgsql-sql(at)postgresql(dot)org
Subject: [SQL] Selecting rows with "static" ordering

Hello,

I have a strange problem (or one that I've never had before anyway). I 
am searching for a list of "id's" for a given table (these id values 
are generated at run-time and held statically in an application-local 
variable).

 From that application, I want to retrieve all those rows, and I want 
them in the order they are currently stored in that variable. So take 
for example this foreign application variable:

   ids = "3,2,5,1,4"

The application then executes this sql:

   select * from table where id in (3,2,5,1,4)

As-is, of course, the above query will return the 5 records in a 
semi-random (i.e. unpredictable/unreliable) order. And I don't want to 
just "order by id" - I want to "order by id(3,2,5,1,4)" (if you see 
what I mean)

Is there a "neat trick" that anyone knows for pulling this off in a 
single query? Basically right now I'm issuing 5 queries to the backend 
to ensure ordering but this horribly inefficient.

Any input or advice would be appreciated,

Steve



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