三种方法

1

SELECT e.last_name, e.first_name, d.dept_no
FROM employees AS e, dept_emp AS d
WHERE e.emp_no = d.emp_no; 

2

SELECT e.last_name, e.first_name, d.dept_no
FROM employees AS e JOIN dept_emp AS d
ON e.emp_no=d.emp_no;

3

SELECT e.last_name, e.first_name, d.dept_no
FROM employees AS e INNER JOIN dept_emp AS d
ON e.emp_no=d.emp_no;