"Jeff Larsen" <jlar310@gmail.com> writes:
> I've noticed that PG automatically creates indexes when you create a
> primary key. But when you create a foreign key on a child table, it
> does not create an index on the referencing columns of the child
> table.
This is intentional since depending on what your workload is like,
the index on the child table might be more overhead than it's worth.
If you frequently do updates or deletes on the parent column, you'll
want to have the child column indexed.
regards, tom lane