With a relational database tables are linked together with relationships. This means that if you alter the contents or structure of a table (such as removing an entry or changing a column name) this can have an effect on other tables. If this happens then steps must be taken to maintain referential integrity.
Example – Pupil and Class table
In the example below we have 2 tables. Each pupil is a member of a class the classID in the pupil table is a foreign key from the class table. This means that the integrity of the pupil table is dependent on the class table.
Referential Integrity compromised
If you alter the contents or structure of the class table then steps must be taken to maintain the referential integrity in the pupil table.