Why 2 queries are fired when calling saveOrUpdate on detached entity

Hibernate ORM
1

This is the code :
Alien alien = session.get(Alien.class, 4);
session.clear();
alien.setTech(“Software11”);
session.saveOrUpdate(alien);
This fires :
Hibernate: select alien0_.aid as aid1_0_0_, alien0_.name as name2_0_0_, alien0_.tech as tech3_0_0_ from Alien alien0_ where alien0_.aid=?
Hibernate: select alien_.aid, alien_.name as name2_0_, alien_.tech as tech3_0_ from Alien alien_ where alien_.aid=?
Hibernate: update Alien set name=?, tech=? where aid=?

For update method :
Alien alien = session.get(Alien.class, 4);
session.clear();
alien.setTech(“Software22”);
session.update(alien);
This fires :
Hibernate: select alien0_.aid as aid1_0_0_, alien0_.name as name2_0_0_, alien0_.tech as tech3_0_0_ from Alien alien0_ where alien0_.aid=?
Hibernate: update Alien set name=?, tech=? where aid=?

Only one query for update which also should hit database as entity is detached and saveOrUpdate does 2 query for same reason why?