Access 2007 Programming by Example with VBA, XML, and ASP

Chapter 20Enforcing Data Integrity and Relationships between Tables

When creating tables in a database, you often need to define rules regarding the values allowed in columns (fields). As mentioned in Chapter 19, constraints allow you to enforce integrity by creating rules for a table. The five types of constraints are listed below.

Table 20-1: Table constraints

Constraint Name	Usage
PRIMARY KEY	Identifies the column or set of columns whose values uniquely identify a row in a table.
FOREIGN KEY	Defines the relationship between tables and maintains data integrity when records are being added, changed, or deleted in a table.
UNIQUE	Ensures that no duplicate values are entered in a specific column or combination of columns that is not ...