How Many Databases are there? I know some of the databases, but i want to know many more databases, & what are they?

Not sure what you mean, but here is a link get to reading

Database can be classified in three major categories.

Flat file database system. -- Old system very redundant, hence not much preferred.

DBMS -- A database that can store your data in rows and column and in ordered way but cant form relations between the tables. These are still in use but i won't suggest it.

RDBMS -- Relational database management system. A system that allows the user to maintain integrity of the data. It allows easy insertion, updation, deletion and backup of data.

There are a lot of database system in the world----- examples

DB2 by IBM
Postgres SQL -- Free and open source
MySQL --- Open Source and widely used in PHP sites
MS-SQL Server -- By Microsoft
MS-Access by Microsoft for general or small scale data handling
Derby --- By Sun Micosystem

and many more. can't name them all