How to add composite primary key to table

Question

create table d(id numeric(1), code varchar(2))

After I create the above table how can I add a composite primary key on both fields and also a foreign key?

Answer 1

alter table d add constraint pkc_Name primary key (id, code)

should do it. There's lots of options to a basic primary key/index depending on what DB your working with.

Answer 2

In Oracle, you could do this:

create table D (
  ID numeric(1),
  CODE varchar(2),
  constraint PK_D primary key (ID, CODE)
);

Answer 3

The ALTER TABLE statement presented by Chris should work, but first you need to declare the columns NOT NULL. All parts of a primary key need to be NOT NULL.