When you are joining 2 datasets from 2 different sources, identical column names are merged and the data appears in one column. However, if one of the data sources has additional columns not in the first data source, the output includes ALL columns from all data sources (ie the superset of columns).
It would be extremely useful to be able to restrict the output to just the columns contained in the first datasource. That way, you do not need additional regex filters or groovy to restrict only to the columns that you need.
