About Constraints

Constraints are conditions which are used when face some problems at designing of database and web pages. Each Constraints defines a subset of the set of all possible designs in which it is satisfied. When several constraints are specified, it is only the possibilities within the intersection of all the subsets that we are interested in. This intersection becomes smaller as more constraints are added. If it becomes empty, then there is no design which satisfies all the constraints. The designer’s skill is now in deciding which constraints it is safe to relax. Constraints are the rules enforced on data columns on table. These are used to limit the type of data that can go into a table. This ensures the accuracy and reliability of the data in the database.