假设数据库表结构如 这里所示

select employees.employees.emp_no, 
    employees.employees.first_name, 
    employees.employees.last_name, 
    employees.salaries.salary
from employees.employees
inner join employees.salaries
on employees.employees.emp_no = employees.salaries.emp_no
limit 500

和

select employees.employees.emp_no, 
    employees.employees.first_name, 
    employees.employees.last_name, 
    employees.salaries.salary
from employees.employees,employees.salaries
where employees.employees.emp_no = employees.salaries.emp_no
limit 500

有哪些区别？