From: Victor Yegorov <viy@pirmabanka.lv>
To: Dan Winslow <danwinslow@cox.net>
Cc: pgsql-sql@postgresql.org
Subject: Re: Seeking help with a query....
Date: Mon, 24 Mar 2003 10:20:14 +0200
Message-ID: <20030324082014.GG20481@pirmabanka.lv> (raw)
In-Reply-To: <gyGea.116460$JE5.71106@news2.central.cox.net>
References: <gyGea.116460$JE5.71106@news2.central.cox.net>
* 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.
>
> Given a table :
>
> create table atable (
> code1 char,
> code2 char,
> cost int
> );
>
> And the rows
>
> code1 code2 cost
> -----------------------------
> a b 2
> d e 4
> b a 6
> f g 1
>
> 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.
--
Victor Yegorov
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To: pgsql-sql@postgresql.org
Cc: viy@pirmabanka.lv, danwinslow@cox.net
Subject: Re: Seeking help with a query....
In-Reply-To: <20030324082014.GG20481@pirmabanka.lv>
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