Microsoft® SQL Server® 2008 Administrator's Pocket Consultant

Column Constraints and Rules

Column constraints and rules are important aspects of database administration. You use constraints to control the way column values are used, such as whether a value must be unique or whether it must have a specific format. Although you usually apply constraints directly to a specific column, you also can use rules to create constraints that you can apply to multiple tables in a database.

Using Constraints

SQL Server enforces the uniqueness of column values using unique and primary key constraints. You will often use unique constraints to create secondary keys (for nonclustered indexes) that you can use in conjunction with the primary key. Foreign key constraints identify the relationships between tables and ensure that ...