Re: Foreign key constraint accepted even when not same - Mailing list pgsql-general

Stephan Szabo <sszabo@megazone.bigpanda.com> writes:
> On Mon, 22 Sep 2003, Jean-Christian Imbeault wrote:
>> Is it right for postgres to accept a foreign key constraint when the
>> type of the field is not the same as that of the foreign key?

> IIRC in SQL92 it's said that they need to be the same type, but in SQL99
> it says that the two types must be comparable.  We basically implement the
> latter, basically using the existance of a usable equality operator as the
> determination of comparable.

Note however that performance may be poor with a cross-type foreign key
reference, if the planner is unable to figure out how to use an index
for the check queries.

            regards, tom lane