这种方式运行出来的性能相对比较差,时间相对慢点方式1:select * from employees where last_name !="Mary" and emp_no%2 !=0 order by hire_date desc 方式二:试用嵌套查询对sql 效率上的提高相对来说会高点select * from employees where emp_no not in (select emp_no from employees where last_name='Mary') and emp_no%2 !=0 order by hire_date desc