pg_constraint

For tracking of Foreign Keys, Check constraints, and maybe NULL / NOT
NULL (specific type of check constraint) I intend to create (as per
suggestion) pg_constraint.

conrelid
conname
contype ('c'heck, 'f'oreign key, ???)
conkey (int2vector of columns of relid, like pg_index.indkey)
connum int4 -- unique identifying constraint number for the relation
id.
consrc
conbin

Dependencies would be on conrelid, and connum in pg_depend.  If each
constraint has a unique number for the relation OIDs aren't required
here.  Much like pg_attribute.

pg_class.relchecks would change to mean relconstraints, though I wont
change the column name.

A view to pg_relcheck would be created.

End result? Foreign Keys will be tracked and restricted / cascaded
through via pg_depend code (see patches archive in April).  This would
knock several items off the TODO list.

I'm not exactly sure how to find out what columns a check constraint
depends on, but I'm sure I'll figure that out sooner or later.

Any thoughts or suggestions?  Is there any reason to allow a check in
a namespace other than the relation it's tied to?  Spec seems to allow
that, but is it actually useful?
--
Rod