Does an index slow down updates on indexed columns?
Yes • what is a constraint? Constraints in Microsoft SQL Server 2000/2005 allow us to define the ways in which we can automatically enforce the integrity of a database. Constraints define rules regarding permissible values allowed in columns and are the standard mechanism for enforcing integrity. Using constraints is preferred to using triggers, stored procedures, rules, and defaults, as a method of implementing data integrity rules. The query optimizer also uses constraint definitions to build high-performance query execution plans.
