Given the following mapping for the parent table (the fact that it is a @Entity, not a @MappedSuperclass is important):
with the following child table:
Hibernate logs the following error when starting the context (and the context is successfully started anyway):
This mapping was OK with Hibernate < 5 and Hibernate should not try to create a contraint for this table.
I will push a test case using the Hibernate templates in a followup comment.