named generic constraints [feature request]

So last time I checked this wasn't possible (at least not that anyone
has told me). I'd like to be able to create constraints that aren't
tied to a specific table/column.

I think that the syntax would look something like this

CREATE CONSTRAINT empty CHECK (VALUE = '\0' );

this should allow us to do thinks like

CREATE TABLE users (             username TEXT NOT empty
);

the example from create domain (modified)  is also pretty good

CREATE CONSTRAINT zip CHECK(  VALUE ~ '^\\d{5}$'
OR VALUE ~ '^\\d{5}-\\d{4}$'
);

-- 
Caleb Cushing

http://xenoterracide.blogspot.com