Ben Leslie <benno@xxxxxxxxxxx> writes: > "Technically, PRIMARY KEY is merely a combination of UNIQUE and NOT NULL" > > I wanted to clarify if that was, technically, true. Yes, but see below. > "identifying a set of columns as primary key also provides metadata > about the design of the schema, as a primary key implies that other > tables can rely on this set of columns as a unique identifier for > rows." This means that e.g. you can use ALTER TABLE othertbl FOREIGN KEY (refid) REFERENCES mytbl without specifying the column(s) of mytbl. This implies that there can be only one primary key (possibly covering more than one column), and that's the second difference to UNIQUE NOT NULL. -- Sent via pgsql-general mailing list (pgsql-general@xxxxxxxxxxxxxx) To make changes to your subscription: http://www.postgresql.org/mailpref/pgsql-general
