Using SQL to Connect Databases
SQL, along with a few specific tools, can connect databases across different database management systems (DBMS). Databases created by different DBMS have their data organized in different ways, and each expects to be talked to in its own way. This is fine if your database application assumes the same DBMS that created your database in the first place. However, that is not always the case. In fact, sometimes your application may want to retrieve data from one database and then retrieve other data from a different database that was created by a different DBMS.
To handle such situations you need something to translate generic database requests into the specific form expected by the database on the back end. Two tools that do this are ODBC and JDBC. What those acronyms originally stood for doesn't really matter. What does matter is what they do. They give your application program a standard interface that looks the same regardless of what database you are accessing:
The ODBC or JDBC translates your standard SQL into the specific dialect expected by the database.
When the database returns a result, the ODBC or JDBC interface becomes active again, passing on the result set to the user.