Re: Cross-table constraints

On Tue, 28 Jan 2003, Rodger Donaldson wrote:

> Now, adding a UNIQUE constraint on the pk for add_queue weeds out
> dupes there.  However, attempting to add a cross-table UNIQUE check
> with:
>
> alter table add_queue add constraint add_queue_no_dupe_sites unique
> (sites.url);
> ERROR:  parser: parse error at or near "."
>
> ,,,fails.  Foreign key constraints will only require a match (of one
> sort or another) in the foreign table, according to the postgresql 7.2
> documentation, and do not have an option to require no match.
>
> Am I missing something obvious (syntax for UNIQUE, for example), or
> trying to do something that just doesn't work that way?

I'm not sure what a unique constraint on sites.url on table add_queue
is supposed to mean precisely.  You can probably come pretty close by
making a set of triggers on both tables however.