Ok. I had read what you posted. When I think of "Joining" two tables, I think of placing both queries into a new query and being able to "join" of link them by a common value.
That would not be what you would do with an update query. That is why I answered your question that way I did.
If you have the two queries that will do what you want, you can automate the execution of those queries with a macro or using VBA code.