> Identity columns don't work if they own more than one sequence.
> test=> INSERT INTO ser (id) VALUES (DEFAULT);
> ERROR: more than one owned sequence found
> I propose that we check if there already is a dependent sequence
> before adding an identity column.
> The attached patch does that, and also forbids setting the ownership
> of a sequence to an identity column.
Alternatively, maybe getOwnedSequence should only consider sequences
with an "internal" dependency on the column. That would avoid the problem
without forbidding anything, since normal OWNED BY dependencies are "auto".