Re: multi column foreign key for implicitly unique columns

В Срд, 18.08.2004, в 04:45, Josh Berkus пишет:
> Markus,

Hi Josh,

> Hey, I see you figured out a workaround to writing a trigger for this.  Let's
> see if we can make it work.
>
> ERROR:  there is no unique constraint matching given keys
>         for referenced table "objects"
>
> The reason for this is that CASCADE behavior gets quite odd when there is an
> FK reference to a non-unique column.   We used to allow it, in 7.1, and I was
> responsible for a number of bug reports that led to us disallowing it.   It
> should be theoretically implementable and relationally sound but will require
> a *lot* of troubleshooting to make work.   So far, nobody's really interested
> enough.
>
> However, you have an easy way out:
>
> ALTER TABLE objects ADD CONSTRAINT obj_unq_2 UNIQUE (name, class_name);

I was worried about the performance hit because (name, class_name) will
always be unique, yet they will be checked for uniqueness.

Thanks

--
Markus Bertheau <twanger@bluetwanger.de>