1. What we normally check for in the Database Testing?

In DB testing we need to check for,
1. The field size validation
2. Check constraints.
3. Indexes are done or not (for performance related issues)
4. Stored procedures
5. The field size defined in the application is matching with that in the db.
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2. What is Database testing?

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.
{mosgoogle left}
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.

3. How to Test database in Manually? Explain with an example

Ans :
Observing that opertaions, which are operated on front-end is effected on back-end or not.
The approach is as follows :
While adding a record thr' front-end check back-end that addition of record is effected or not.
So same for delete, update,......

Ex:Enter employee record in database thr' front-end and check if the record is added or not to the back-end(manually).