Eine Einführung in
A composite key has more than one attribute (field). In this example we store details of tracks on albums - we need to use three columns to get a unique key - each album may have more than one disk - each disk will have tracks numbered 1, 2, 3...
The primary key must be different for each row of the table. The primary key may not contain a null.
|Specific to DB2|
|We must explicitly state that the components are NOT NULL.|