Date: Mon, 24 Mar 2003 10:20:14 +0200
From: "Victor Yegorov" <viy@pirmabanka.lv>
To: "Dan Winslow" <danwinslow@cox.net>
Cc: pgsql-sql@postgresql.org
Subject: Re: Seeking help with a query....
Message-ID: <20030324082014.GG20481@pirmabanka.lv>
Mail-Followup-To: "Dan Winslow" <danwinslow@cox.net>, pgsql-sql@postgresql.org
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* Dan Winslow <danwinslow@cox.net> [21.03.2003 21:58]:
> Hi folks, seeking help with a query that I thought was simple, but
> apparantly isn't, at least for someone with my knowledge level.
>=20
> Given a table :
>=20
> create table atable (
>   code1 char,
>   code2 char,
>   cost    int
> );
>=20
> And the rows
>=20
> code1    code2    cost
> -----------------------------
> a            b            2
> d            e            4
> b            a            6
> f            g            1
>=20
> I need a ( preferably single ) query that will sum the costs for any
> matching pairs of codes regardless of order. That is, row 1 and row 3
> concern the same pair of unordered codes (a,b), and the result should show
> that the (a,b) pair had a summed cost of 8. I am not able to change any of
> the environment or preconditions other than the query itself. I have tried
> so many approaches that they aren't even worth listing. Any suggestions
> would be very much appreciated.

First thing, that came to my mind:

Give each code (if they are not numeric) a number. For this example, that
could be ASCII code of chars. Create view on that table:

CREATE VIEW aview AS
	SELECT at.*, code(at.code1) + code(at.code2) AS dbl_code FROM atable at;

dbl_code field will have equal values for all groups of codes with same
codes involved: a and b, b and a.

About function code() I used to create the View: it's just an assumption,
you should write one yourself (on C for faster perfomance). Or simply use:

code1 + code

if your codes are of numeric type and are foreign keys to some other table's
primary key.


Please, give some feedback on usability of this solution.

--=20

Victor Yegorov

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