On Mon, Jun 5, 2017 at 5:40 PM, John R Pierce <pie...@hogranch.com> wrote:

> ​i​
> ndeed, any sort of constraint that invokes a function call which looks at
> other tables could later be invalidated if those other tables change, and
> postgres would be none the smarter.   the same goes for trigger based
> checks.
>

​Yes.  I could imagine a new kind of "multi-referential trigger" that would
specify all relations it touches and the function to fire when each of them
is updated.  While you'd still have to write the functions correctly it
would at least allow one to explicitly model the multi-table dynamic in
pg_catalog.  Lacking that CHECK is no worse than TRIGGER and we've decided
to say "use triggers".

David J.​

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