Re: assertions and constraint triggers

On 8/11/10 8:31 AM +0300, Peter Eisentraut wrote:
> Thinking about SQL assertions (check constraints that are independent of
> one particular table), do you think it would be reasonable to implement
> those on top of constraint triggers? On creation you'd hook up a
> trigger to each of the affected tables. And the trigger function runs
> the respective check expression. Conceptually, this doesn't seem to be
> very far away from foreign key constraints after all.

I thought the point of ASSERTIONs was that you could write a thing such as:

CREATE ASSERTION foo CHECK ((SELECT count(*) FROM tbl) = 4);

Enforcing that kind of constraints without true serializability seems
impractical.

Regards,
Marko Tiikkaja