FOREIGN TABLES is a rather fresh feature in IRIS  (2023.?)
So I was motivated to try something new by own hands.
Documentation of Foreign Table from File is a good starting point.
Also the related promotional video is fine to start with.

The  advantages of the approach are pretty obvious to me

• differently to SQL LOAD DATA data remain outside IRIS
• you pick out what is useful to you and leave the remaining junk aside
• this seems to be especially attractive for UPDATE and ADD-ON data
• when you are done you have no pollution of your IRIS instance

On my way to create the example I met some facts that I want to share

• The requirement of a JAVA language server is only mentioned in LOAD DATA
  • You fail at first access  if it is missing.  Docker Containers have it.
  • My personal environment doesn't need it.
• Next surprise: What is this FOREIGN SERVER for?
  • Just a placeholder to point to your directory of your CSV-file
• Creation of the TABLE is pretty straight forward and very flexible
• Skipping USING clause presented my headers as first ROW of the table
• And as it's no real table and had no ROW numbers I missed my numeric ID's
• No surprise: It is READ ONLY, No Updates
• Also: Finding the right mix of single and double quotes is some challenge
• Similar: Data presentation in CSV can be tricky
  • Most simple approach: - thinking of date formats -
  • Declare critical columns as VARCHAR 
  • Then handle useful transformations or content check locally  
• Finally:
  • the Table is visible for SQL but there is no related Class to it
  • you have no chance to play with CALCULATED properties

Summary

• A great and highly useful feature
• You have to understand the limits
• Adjust your expectations to the available options
• Test also the "impossible" combinations - they will pop up

Enjoy the demo package
GitHub