Cc: pgsql-sql@postgresql.org
Message-Id: <24123985-9812-49FE-B422-31E7AC963758@rvt.dds.nl>
From: Ries van Twisk <pg@rvt.dds.nl>
To: Mario Splivalo <mario.splivalo@megafon.hr>
In-Reply-To: <4AAE43F8.4000107@megafon.hr>
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Subject: Re: CHECK constraint on multiple tables
Date: Mon, 14 Sep 2009 08:27:53 -0500
References: <4AAE43F8.4000107@megafon.hr>

can't you solve it creating a reference between the tables?

Ries
On Sep 14, 2009, at 8:24 AM, Mario Splivalo wrote:

> I have two tables, tableA and tableB:
>
> CREATE TABLE tableA (idA integer primary key, email character varying
> unique);
> CREATE TABLE tableB (idB integer primary key, email character varying
> unique);
>
> Now, I want to create check constraint in both tables that would
> disallow records to either table where email is 'mentioned' in other  
> table.
>
> If CHECK constraints supported SUBSELECTS, I could write:
>
> ALTER TABLE tableA ADD CONSTRAINT tableA_chk CHECK
> (email NOT IN (SELECT email FROM tableB));
>
> Unfortunatley, postgres won't allow me to do so.
>
> Now, i could create function, check_for_email, that would return  
> TRUE if
> email is mentioned in either table, and then call that function when
> creating a check constraint.
>
> Or I could add separate table, emails, like this:
>
> CREATE TABLE emails (email_id integer primary key, email character
> varying unique)
>
> And then replace 'email' column in tables tableA and tableB with
> 'email_id' that would be foreign key refference to the emails table.
>
> I could, also, write functions for inserting data to the tableA and
> tableB tables.
>
> What would be the best approach to solve the problem I have? Could I  
> use
> rules on insert to help me?
>
> 	Mario
>
> -- 
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			regards, Ries van Twisk

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