I have an application server that currently has 8.1.7 client fully installed and 9.1.2 partially installed. The actual database is 9i

I am trying grasp what the difference is between the two client in terms of sql queries.

If I have 9i SQL query such as a CASE, would the 8.1.7 client have problems dealing with this query?

My senior dba is telling me that client only manages communication and that you can send whatever query you like.

My external software consultant is telling me that 9.1 should allow me to run the newer 9i commands.

Please comment