题解 | #查找入职员工时间排名倒数第三的员工所有信息#用窗口函数
删除emp_no重复的记录，只保留最小的id对应的记录。
http://www.nowcoder.com/practice/3d92551a6f6d4f1ebde272d20872cf05
with em_ra as
(
select *,
row_number() over (partition by emp_no order by id) as rn
from titles_test
)
delete
from titles_test
where id IN (select id from em_ra where rn <> 1);
用row_number()给id从小到大标注，然后把除了第一个的记录删掉