"Database testing" as you've used it covers testing every single aspect of the database, and all connection methods to the database. If you have some marketing requirements or a specific question, please post that. Otherwise you will not get a very good answer to your questions.
Depends to which levels of database testing. I am in database testing team, and mainly testing, database drivers for DB2, UDB, Oracle, and SQL Server which will compatible with our drivers. Testing involved internal and external changes of those drivers. Database testing could involve the integration and performance testing from your client machine to Enterprise server, web sphere, and the database server. Not much on actual data, but metadata and table specifications. For example, Oracle 9I no longer support LONG Raw, extensive testing are required in order to make sure any table that contain BLOB column will not breaks, and this kind of testing will be performed across all the databases except SQL Sever.
Database testings are broad and deep.
How many ways can I break your code
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