ASA SQL User's Guide
  Ensuring Data Integrity
    Data integrity overview

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 dept_id 200) to the department table of the organization's database.

Foreign key relations invalidated 

• The department identified by dept_id 300 closes down and one employee record inadvertently remains unassigned to a new department.