Re: Composite primary keys

Joshua Tolley <eggyknap(at)gmail(dot)com> writes:
> Primary keys are NOT NULL and UNIQUE. You can't have null values in a primary
> key.

On reflection I think the OP's beef is that we complain about this:

regression=# create table t (f1 int null not null);
ERROR: conflicting NULL/NOT NULL declarations for column "f1" of table "t"

but not this:

regression=# create table t (f1 int null primary key);
NOTICE: CREATE TABLE / PRIMARY KEY will create implicit index "t_pkey" for table "t"
CREATE TABLE

even though the implied NOT NULL is really a conflict. I think we could
fix that case if we cared to. However, since the NULL clause is
forgotten about after parsing, there isn't anything we could do to raise
a complaint about doing it in two steps:

regression=# create table t (f1 int null);
CREATE TABLE
regression=# alter table t add primary key(f1);
NOTICE: ALTER TABLE / ADD PRIMARY KEY will create implicit index "t_pkey" for table "t"
ALTER TABLE

(barring remembering the NULL clause in the catalogs, which seems
entirely silly). So I'm not sure how interesting it is to complain
about the single-command case.

regards, tom lane