Hi,
from postgres docs: "foreign key must reference columns that either are a primary key or form a unique constraint". It does not allow creating foreign key constraint on non-unique column - an error is raised.
After playing with a new database I discovered that such a unique constraint can be droped after the foreign key constraint has been established. No warning, no error.
Is such a behaviour intended? I have found no references in the docs.
Thanks.
Vladimir
