If you have @oneToOne
mapping set to FetchType.LAZY
and you use second query (because you need Department objects to be loaded as part of Employee objects) what Hibernate will do is, it will issue queries to fetch Department objects for every individual Employee object it fetches from DB.
Later, in the code you might access Department objects via Employee to Department single-valued association and Hibernate will not issue any query to fetch Department object for the given Employee.
Remember, Hibernate still issues queries equal to the number of Employees it has fetched. Hibernate will issue same number of queries in both above queries, if you wish to access Department objects of all Employee objects