While adding such a configuration option would certainly be a start, allowing us to create the temporary tables out-of-band, I’m still not sure why the temporary tables are necessary in the first place. As described in https://hibernate.atlassian.net/browse/HHH-15517, Hibernate 5 performed our insert into ... select without resorting to temporary tables…

Are you looking into restoring the previous behavior as well, or should I open a separate issue for that?