Question:
How do I define an external table (that is not in my current database) in Informix and access the data in it?

Answer:
If you’re connecting to an external Informix database, assuming that you have the proper I-Connect links between the systems, you would access the remote table as follows:

SELECT * from database@server_name:table_name;

If it’s a non-Informix database you want to connect to, explore the virtual table interface (VTI)—if you’re on an engine beyond the 7-series.