Primary keys

When you assign a primary key to an attribute, the key uniquely identifies the object that is associated with that attribute. The value in the primary column determines which attributes are used to create the primary key.

By default, a primary key is automatically created by taking the object name, adding an ID to the object name, and assigning a primary column value of 1. If you change the value, it must be sequential, unique, and greater than 0. The sequence determines the order in which the primary index is created. Each attribute can have only one primary key. The same attribute can be used in more than one primary key. When the object is saved, the primary key can no longer be modified.

A primary index is automatically created for the primary key and ensures that the primary key is unique. You can use the primary index to retrieve and access objects from the database. The unique index is a column, or an ordered collection of columns, for which each value identifies a unique row. The sequential values that are assigned in the primary columns determine the order in which the unique index is created. A unique index can contain NULL values.