Creating Primary Keys

Each row in a table is uniquely identified by its primary key.

The CREATE TABLE and ALTER TABLE statements allow many attributes of tables to be set, including column constraints and checks.

Creating a Primary Key

The following statement creates the same skill table as before, except that a primary key is added:

CREATE TABLE skill (
  skill_id INTEGER NOT NULL,
  skill_name CHAR( 20 ) NOT NULL,
  skill_type CHAR( 20 ) NOT NULL,
  primary key( skill_id )
)

The primary key values must be unique for each row in the table which, in this case, means that you cannot have more than one row with a given skill_id.

Columns in the primary key are not allowed to contain NULL. You must specify NOT NULL on the column in the primary key.