Re: Check constraints on partition parents only?

This approach certainly can't work, because a table can be both an
inheritance parent and an inheritance child.  It could have an ONLY
constraint, and also inherit a copy of the same constraint for one or
more parents.  IOW, the fact that conislocal = true does not mean that
coninhcount is irrelevant.  

I think what you probably want to do is
either (a) add a new column or (b) change conislocal to a char value
and make it three-valued:

n = inherited constraint, no local definition
o = defined locally as an "ONLY" constraint
i = defined locally as a non-ONLY constraint

I think I favor the latter approach as more space-efficient, but I
hear Tom muttering about backward-compatibility...