I'd like to re-iterate the request for calculated values in a join.
Yes, it can be done in a different SQL editor, or by changing the Query Builder to Custom SQL - but there's more power to Query Builder than just easy query construction. It provides a fast and easy way to create a pretty complicated filter dialog. I could edit the custom SQL to join upper(tb1.field) on upper(tb2.field), or add TO_NUMBER or CAST in the SELECT - but then I loose all the filter GUI portion. I could build an app to do it - but that seem like reinventing what's already there.
For that matter, TO_NUMBER isn't in the calculated field options.
Charles