Add check constraints

- [Instructor] There is one more type of constraint … that I want to talk about … and that's a check constraint … or what's sometimes referred to as … an integrity constraint or a validation rule, … depending on the RDBMS platform that you're working with. … Like null constraints, default values, … and unique constraints, … check constraints are built right into … the design of the table itself … then anytime data is entered into the table, … the database management system … will verify the new values … meet the criteria that have been established. … For numerical data, … you can check that the values … fall within a range of acceptable values. … For instance, a products price must be above zero … and therefore, can't be negative … or an employee's job rating … must be between one and five. … Many of these kinds of data constraints … will be dictated by your business roles. … For character data types, … it's rare that you would specify an alphabetical range … but you can create a check constraint …