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About primary keys

Each table should include a field or set of fields that uniquely identifies each record stored in the table. This information is called the primary key and enforces the entity integrity of the table. A table can have only one primary key constraint, and a column that participates in the primary key constraint cannot accept null values. Because primary key constraints ensure unique data, they are often defined for identity column. An AutoNumber field can be set to automatically enter a sequential number as each record is added to the table. Designating such a field as the primary key for a table is the simplest way to create a primary key.

If a primary key constraint is defined on more than one column, values may be duplicated within one column, but each combination of values from all the columns in the primary key constraint definition must be unique.


Related Topics:

How to create an index

Set or change the primary key

Autonumbering and identifier columns

About indexes

About Indexes Manager

Create and change indexes

Columns

About tables

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