java - What is the difference between select and subselect in Hibernate's fetch attribute? Are there any usage scenarios?

Question

As mentioned, thank you for your advice

Answer 1

• SUBSELECT: avoids N+1 and does not duplicate data, but loads all entities of related types into memory.

FetchMode.SUBSELECT should look like this:

SELECT <employees columns>
FROM EMPLOYEE employees0_
WHERE employees0_.DEPARTMENT_ID IN
(SELECT department0_.DEPARTMENT_ID FROM DEPARTMENT department0_)

FetchMode.SUBSELECT can significantly reduce the number of queries

I found a very good article