How data can become invalid
Here are a few examples of how the data in a database may become invalid if proper checks are not made. You can prevent each
of these examples from occurring using facilities described in this chapter.
Incorrect information
- An operator types the date of a sales transaction incorrectly.
- An employee's salary becomes ten times too small because the operator missed a digit.
Duplicated data
- Two different people add the same new department (with DepartmentID 200) to the Departments table of the organization's database.
Foreign key relations invalidated
- The department identified by DepartmentID 300 closes down and one employee record inadvertently remains unassigned to a new
department.
