Primary, Alternate, and Foreign Keys (PDM)

A key is a column, or a combination of columns, that uniquely identifies a row in a table. Each key can generate a unique index or a unique constraint in a target database.

You can create the following types of keys:

Primary keys - Contain one or more columns whose combined values uniquely identify every row in a table. Each table can have only one primary key.
Alternate keys - Contain one or more columns whose combined values uniquely identify every row in a table.
Foreign keys - Contain one or more columns whose values match a primary or alternate key in some other table.

In the following example, the TITLE table has a primary, alternate and foreign key:

The primary key, TITLE_ID contains the column TITLE ISBN, and uniquely identifies each book in the table.
The alternate key, TITLE_NAME, contains the columns TITLE NAME and TITLE TYPE, and enforces a constraint that no two titles of the same type can have the same name.
The foreign key contains the column PUBLISHER ID and references the primary key column in the Publisher table.

Creating Primary Keys
A primary key is the primary identifier for a table, and is attached to one or more columns whose combined values uniquely identify every row in the table. Every table must have a primary key.
Creating Alternate Keys
An alternate key is a key associated with one or more columns whose values uniquely identify every row in the table, but which is not the primary key. For example, where the primary key for a table may be the employee id, the alternate key might combine the first, middle, and last names of the employee. Each alternate key can generate a unique index or a unique constraint in a target database.
Creating Foreign Keys
A foreign key is a primary or alternate key migrates from another table. Foreign keys are generally migrated automatically when you draw a reference from a child to a parent table.
Key Properties
To view or edit a key's properties, double-click its Browser or list entry. The property sheet tabs and fields listed here are those available by default, before any customization of the interface by you or an administrator.

Parent topic: Physical Diagrams