I was wondering if someone could help point me in the right direction
w.r.t. foreign unique constraints. I'm working on a legacy database
and have a new requirement and am not sure how to do it.
I have something like this
create table table1 (
id SERIAL PRIMARY KEY
extension UNIQUE,
<other fields>
)
create table table2 (
id SERIAL PRIMARY KEY
extension UNIQUE,
<different fields>
)
Basically table 1 and table 2 both have the concept of an extension
that must be unique but the rest of the info in the tables are
different. I need to ensure that if i add an entry to table 1 with
extension 1000 that it will fail if there is already an entry in
table2 with the same extension.
Essentially i need to do something like the following but i get errors
saying this can't be done.
alter table table1 add check (extension <> table2.extension);
It should be noted i am using pg version 7.4.13 and this can't change.
Thanks for any help you can offer.
Jon.