If a relational table is in a query, then it is not possible to delete the relational table.

The error message:

"Unable to delete contact source. Contact source has references in one or more of the following:
mailing queries"

To delete this relational table, I have to find all of the queries and remove the relational table from those.

There is no option to find them. It would be great to have an API-Call or something in the user interface.