WHERE限定

可以直接使用WHERE限定语句
SELECT d.dept_no, d.emp_no, s.salary
FROM dept_manager AS d, salaries AS s
WHERE d.emp_no = s.emp_no
AND d.to_date = s.to_date
AND d.to_date = '9999-01-01'

也可以使用 INNER JOIN
SELECT d.dept_no, d.emp_no, s.salary
FROM dept_manager AS d INNER JOIN salaries as s
ON d.emp_no = s.emp_no
AND d.to_date = s.to_date
AND d.to_date = '9999-01-01'