Harald Fuchs <hari.fuchs@xxxxxxxxx> writes: > 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." Yeah. The extra metadata has several other effects. Perhaps it would be better to reword this sentence to make it clear that PRIMARY KEY is equivalent to UNIQUE+NOTNULL in terms of the data constraint that it enforces, without implying that there is no other difference. I'm not sure about a short and clear expression of that though ... 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
