hibernate update vs JPA merge on detached instance

问题

Both will update the persistent state but

• merge will return attached instance letting the given one unchanged.
• update will attach the given instance

my question is so : will JPA merge also trigger a select (i suppose it will to get the attached instance) whereas hibernate update won't ?

please don't try to explain me things that can already be found here What are the differences between the different saving methods in Hibernate?

来源：https://stackoverflow.com/questions/22459233/hibernate-update-vs-jpa-merge-on-detached-instance