Re: CHECK constraint on multiple tables

How would you do it, without creating third table?

Mario

Ries van Twisk wrote:
> 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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