Re: NOT NULL constraints in foreign tables

On 17-08-2012 16:44, Robert Haas wrote:
> On Fri, Aug 17, 2012 at 2:58 PM, Alvaro Herrera
> <alvherre@2ndquadrant.com> wrote:
>> I mean, what are NOT NULL in foreign tables for?  Are they harmed or
>> helped by having pg_constraint rows?
> 
> As I've mentioned when this has come up before, I think that
> constraints on foreign tables should be viewed as declarative
> statements about the contents of the foreign data that the DB will
> assume true.  This could be useful for a variety of purposes:
> constraint exclusion, query optimization, etc.
> 
+1. I don't see us providing a mechanism to cross-check changes between data
sources. Even if we do it for creation time, schema could be changed behind
the scenes. Let's use at least constraints (NOT NULL, CHECK, UNIQUE, PK --
UNIQUE + NOT NULL) to improve optimizer but warn (loudly) that those
constraints are merely for optimization.


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