How do I join two tables on two different instances of DB2? There are two instances of DB2 running on the same machine. One has a table aliased to the a table in the other one.  Is there a way to do this in DB2 or does it have to be done via an external tool?

This is with an older version of DB2
The "federation" feature in DB2 will allow you to do what you need.

It's available on the Linux/Unix/Windows version of DB2 - not sure about the mainframe - and there are no licensing issues, it's part of the base product set.

To implement it you only need to create a few extra db objects (wrapper, server mappings, nickname) and you're more or less done.  Follow the documentation and you should be fine.

Cheers.