On Mon, Jul 28, 2003 at 09:26:33 +0530,
>
> Primary key is the combination of unique index + not null. In your case,
> both are listed. For further details refer pg_indexes system view.
That isn't the whole story. The primary key of a table is also a default
for foreign keys. There can be several columns that have a unique index
and a not null constraint, but there can be only one primary key.
(The primary key can also be multicolumn.)