sql
create table Person(
    id int primary key,
    email varchar(20)
) ;

<!-- more -->

show tables;

drop table Person;

insert into Person values (1,'join@qq.com'),(2,'join@qq.com'),(3,'qwm@qq.com');
insert into Person values (5,'xwm@qq.com');
delete p1 from Person 
as p1,Person p2 where 
p1.email = p2.email 
and p1.id > p2.id;

delete from Person where
id not in (select id from
(select min(id) as id from
Person group by email) t);


select p1.email from Person as p1,
Person as p2 where p1.email=p2.email 
and p1.id!=p2.id group by p1.email;

select email from
Person group by email 
having count(email) > 1;

总结

• group by + having解决重复小妙招