From: PFC <lists@boutiquenumerique.com>
To: Bruno Wolff III <bruno@wolff.to>
Cc: Stefan Weiss <spaceman@foo.at>
Cc: pgsql-sql@postgresql.org
Subject: Re: Links between rows in a table
Date: Mon, 07 Mar 2005 19:41:25 +0100
Message-ID: <opsm957bpsth1vuj@musicbox> (raw)
In-Reply-To: <20050307161555.GA3643@wolff.to>
References: <422A8A26.1070704@foo.at>
<20050306174201.GA19019@wolff.to>
<422B4B9A.8020606@foo.at>
<opsm8dm0z7th1vuj@musicbox>
<20050307161555.GA3643@wolff.to>
> The trouble with this approach is that for some ways of using this data
> you will need to worry about the ordering of of the values.
Tradeoffs, always tradeoffs...
It depends on the application. Note also that it eliminates duplicates ;
moreover without such a condition, any relation A-B could have the rows
[(A,B)] or [(B,A)] or [(A,B),(B,A)] which promises to cause headaches if
you need to get rid of the duplicates...
I used this scheme for an "also purchased products" thingy on a website,
it works well. In this case the row must be unique because we have
(A,B,count) which is the number of times products A and B have been
purchased together, in this case having rows (B,A) and (A,B) separated
wouldn't help in sorting by this count, which is in my case very fast
thanks to a multicolumn index.
> Note that you can't literally use 'min' and 'max' as above, as those
> functions
> don't do that. You could use 'case' to do that.
... yes, it was just a way of saying it. You can define functions that
take integers as arguments (I wish these basic bricks were defined by
default)...
>
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To: pgsql-sql@postgresql.org
Cc: lists@boutiquenumerique.com, bruno@wolff.to, spaceman@foo.at
Subject: Re: Links between rows in a table
In-Reply-To: <opsm957bpsth1vuj@musicbox>
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