Sorry for the misunderstanding. When you are [creating or editing a Join View](https://community.denodo.com/docs/html/browse/6.0/vdp/administration/creating_views/creating_derived_views/creating_join_views#creating-join-views) in the VDP Administration Tool, you should be able to see the data types of all the component view columns right on the *Model* tab. I would use the [Request Monitoring](https://community.denodo.com/docs/html/browse/6.0/vdp/dmt/monitoring/monitoring_servers/monitoring_requests) in the Denodo Diagnostic & Monitoring Tool to identify which queries are seeing the performance hit to determine which Derived View Models need to be inspected to validate data type matching (or other performance issues). The user interface of the Administration Tool is your best tool for this, as the joins are defined in the VQL CREATE VIEW statement and not in a columnar format you can query.
Hope this helps!