If they're not, the below causes problems, as the foreign key is added

after the CHECK.  Cluster depends on the index name, so I thought it
wise to ensure all names are available, rather than leaving off the
CONSTRAINT "$n" portion for internally named constraints.

CREATE TABLE jkey (col integer primary key);
CREATE TABLE j (col integer REFERENCES jkey);
ALTER TABLE j ADD CHECK(col > 5);

This is a problem in 7.3 series as well as -Tip.

Rod Taylor <rbt@rbt.ca>