Microsoft® SQL Server™ 2000 Unleashed, Second Edition

Rules

Rules are used to limit the range of values that can be stored in a column. They are similar to CHECK constraints in this regard, but they are more limited in their functionality. A rule is considered a bound object; that is, the rule is first created, and then is bound to a column or User-Defined Datatype.

Rule Usage

A rule, once created, can be bound to multiple columns or User-Defined Datatypes (UDTs). A rule can be useful to maintain consistency not just in a column, but in all columns and UDTs across the database to which it is bound. For example, if you require a standard format for telephone numbers, you could create the following rule:

 CREATE RULE phone_rule AS @phone LIKE '([0-9][0-9][0-9]) [0-9][0-9][0-9]-[0-9][0-9][0-9][0-9]' ...