In my original test, I've used native queries to populate the database because it was a quick draft to provide a test case.
It seems that the approach I've used doesn't work in Oracle, though: https://github.com/hibernate/hibernate-reactive/actions/runs/12869137204/job/35877269478#step:8:1496

Could you update the test case so that it works with all the databases? Ideally without native queries.

Merged, thanks a lot!