What is database testing and what we test in database testing?

An1:
Database testing is all about testing joins, views, inports and exports , testing the procedures, checking locks, indexing etc. Its not about testing the data in the database.
Usually database testing is performed by DBA.

An2:
Database testing involves some in depth knowledge of the given application and requires more defined plan of approach to test the data.
Key issues include:
1) Data Integrity
2) Data Validity
3) Data Manipulation and updates
Tester must be aware of the database design concepts and implementation rules.

An3:
Data bas testing basically include the following.
1)Data validity testing.
2)Data Integritity testing
3)Performance related to data base.
4)Testing of Procedure,triggers and functions.
for doing data validity testing you should be good in SQL queries
For data integrity testing you should know about referintial integrity and different constraint.
For performance related things you should have idea about the table structure and design.
for testing Procedure triggers and functions you should be able to understand the same.