ADD key CONSTRAINTs to a table

You can add the PRIMARY KEY keyword after the column_name that should be unique. This, of course, only works for new tables

CREATE TABLE products(
  product_no integer primary key,
  name text,
  price numeric
)


or

CREATE TABLE products(
  product_no integer,
  name text,
  price numeric,
primary key(product_no, name)
)

To add a primary key to an existing table. You add it by:

ALTER TABLE table_name
ADD CONSTRAINT some_name PRIMARY KEY (column_name)


ALTER TABLE universities
ADD CONSTRAINT university_pk PRIMARY KEY (id);