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From: Josh Berkus <josh@agliodbs.com>
Reply-To: josh@agliodbs.com
Organization: Aglio Database Solutions
To: "Patrick Hatcher" <PHatcher@macys.com>, pgsql-sql@postgresql.org
Subject: Re: Is it possible to use a field from another table as part of a
	query?
Date: Fri, 19 Jul 2002 11:54:27 -0700
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Partick,

> I have a table that contains a VARCHAR field with data formatted as such:
> 12,44,13,225
> what I would like to do is use this field in a query to another table such
> as:

1. Since you are a smart guy, I'm assuming that this "delimited" VARCHAR da=
ta=20
is legacy data that you don't have a choice about re-structuring.  Because,=
=20
of course, the normalized way to store the data would be in a subtable, not=
 a=20
VARCHAR field.

>=20
> CREATE TABLE category_tree (
>   tree varchar(200)
> ) WITH OIDS;
>=20
> Select * from mdc_products
> where keyf_category_home IN  (select tree from category_tree)
>=20
> However, my keyf_category_home field is an INT4.  Is there a way to parse
> out the tree field so that I can define it as INT4?

Well, this is easiest thing to do:

Select * from mdc_products
 where EXISTS=20
	(select tree from category_tree
		WHERE tree ~ ('(^|,)' || keyf_category_home || '(,|$)'));

(somebody please correct my regexp if I've made an error)

... but that's impossible to index.   If the table category_tree doesn't=20
change often, I'd write a program to parse the data and build a normalized=
=20
subtable containg a vertical colum of tree values.

--=20
-Josh Berkus
 Aglio Database Solutions
 San Francisco