MySQL学习疑问1

为什么一下这两句话执行的结果不一样？请教路过的大佬们解答下我的疑惑

select * from employees where department_id < 90 or department_id > 110 or salary > 15000;
select * from employees where (department_id < 90 or department_id > 110) or salary > 15000;