Paul Hartley <phartley@xxxxxxxxx> writes: > ... I'm unclear > if PostgreSQL treats primary keys differently from unique, non-null > constraints. The *only* thing that the system does specially with a primary key constraint is that a PK creates a default column target for foreign key references. For example, create table m (id int primary key); create table s (refid int references m); versus create table m (id int); create unique index mi on m (id); create table s (refid int references m(id)); I have to spell out "(id)" in that last command because there's no PK to establish a default target. Other than that, behavior and performance should be the same. The planner and executor only care about the indexes, not about whatever constraints they might have come from. Likewise, NOT NULL is NOT NULL regardless of what syntax you used to slap it onto the column. regards, tom lane -- Sent via pgsql-general mailing list (pgsql-general@xxxxxxxxxxxxxx) To make changes to your subscription: http://www.postgresql.org/mailpref/pgsql-general
