文章目录

• ​​计算特殊奖金​​
• ​​变更性别​​
• ​​删除重复的电子邮箱​​

计算特殊奖金

select employee_id,
case when (employee_id%2)=1 and name not like 'M%'
then salary else 0 end
as bonus
from Employees
order by employee_id;

变更性别

使用update交换性别

update salary set sex = if(sex = 'm','f','m');

update salary set sex = (
    case sex when 'm' then 'f' else 'm' end
);

删除重复的电子邮箱

内连接，笛卡尔积

select * from person a inner join person b;

select * from person a inner join person b on a.email = b.email;

select * from person a inner join person b on a.email = b.email and a.id > b.id;

delete a from person as a inner join person as b on a.email = b.email and a.id > b.id;

delete from person where id not in (select id from (select MIN(id) as id from person group by email) as tmp);