A primary key constraint is a key that uniquely identifies a record in a database and is the primary point of access to that record. Unlike some other constraints, a table can have only one primary key.

Because a primary key constraint ensures unique data, it is frequently used in conjunction with an identity column (Identity Column Constraints ).

RWDBPrimaryKey encapsulates a primary key. A primary key is composed of a collection of RWDBColumn instances and must contain at least one column. You can assign a constraint name to the primary key or let the database assign one.