关于LEFT OUTER JOIN ... ON还是 RIGHT OUTER JOIN ... ON 建议只记 LEFT OUTER JOIN ... ON 最终返回的行数都由FROM的那个表决定 SELECT last_name,first_name,dept_no FROM dept_emp LEFT OUTER JOIN employees ON employees.emp_no = dept_emp.emp_no dept_emp两行,所以呢最终返回两行 SELECT last_name,first_name,dept_no FROM employees LEFT OUTER JO...