Обсуждение: Is it possible to use a field from another table as part of a query?

I originally sent this question to the Novice group, but realized I should
have asked it here:

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:

CREATE TABLE category_tree ( tree varchar(200)
) WITH OIDS;

Select * from mdc_products
where keyf_category_home IN  (select tree from category_tree)

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?
TIA

Patrick Hatcher

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 data
is legacy data that you don't have a choice about re-structuring.  Because,
of course, the normalized way to store the data would be in a subtable, not a
VARCHAR field.

>
> CREATE TABLE category_tree (
>   tree varchar(200)
> ) WITH OIDS;
>
> Select * from mdc_products
> where keyf_category_home IN  (select tree from category_tree)
>
> 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_productswhere EXISTS (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
change often, I'd write a program to parse the data and build a normalized
subtable containg a vertical colum of tree values.

--
-Josh BerkusAglio Database SolutionsSan Francisco