There are times when you need to query tables from different Database Management Systems (DBMSs). For example, one type of information or data may reside in DB2 UDB table and another in DB2 for z/OS or even Oracle table. How will you write queries that joins these tables and fetches the desired results?
The answer is 'federation'. If you have DB2 UDB, and want to join a table from Oracle or DB2 for z/OS, create a federated table image of the table that resides in the other DBMS. Once you create a federated table, you can write queries treating it like a table that resides on the local DB2 UDB server.
For example:
SELECT L.col1, L.col2, F.cola, F.colb
FROM Local_Table L, Federated_Table F
WHERE L.col3 = F.colc
Remember that for "federation" to work, you need DB2 Connect or a similar product.
You can find more details here:
IBM Federated Database Technology
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