Investigating+database+anomalies

Introduction
There are 3 main types of anomaly which can occur in a flat-file database. See if you can spot the three different types of data anomalies by completing the tasks below:

Task 1:
Mr O'Hara is a teacher in the English department and he teaches in English Room 4. Add Mr O'Hara's details to the database.

What problem does this raise?

Task 2:
The art department is reorganising rooms and Miss Dewar is moving from Art Room 3 to Art Room 1. Update the database to show this.

Can you see where this might create a problem?

Task 3:
John McGinn has left school. Delete his record from the database.

What problem does this cause?