mysql数据库删除重复数据只保留一条方法实例

create database mysql_exercise charset utf8;

create table users(
					id int auto_increment primary key,
					identity_id varchar(20),
					name varchar(20) not null
     );

insert into users values(0,'620616199409206512','张三'),
						(0,'620616199409206512','张三'),
						(0,'62062619930920651X','李四'),
						(0,'62062619930920651X','李四'),
						(0,'620622199101206211','王五'),
						(0,'620622199101206211','王五'),
						(0,'322235199909116233','赵六');

delete from users where id not in (select max(id) from users group by identity_id,name);

select max_id from (select max(id) as max_id from users group by identity_id,name);

select t.max_id from (select max(id) as max_id from users group by identity_id,name) as t;

delete from users where id not in (
		select t.max_id from 
		(select max(id) as max_id from users group by identity_id,name) as t
		);

update user_info set status='0' where user_id in (select user_id from user_info where name='')

update user_info set status='0' where user_id in 
	 (select user_id from (select user_id from user_info where name = '') t1);

update user_info set status='0' where user_id in 
	(select t1.user_id from (select user_id from user_info where name='') as t1);

select user_id from user_info where name='';

select user_id from (select user_id from user_info where name='') as t;

update user_info set status='0' where user_id in 
	(select user_id from (select user_id from user_info where name='') as t1);

+----+------------------+
| Id | Email      |
+----+------------------+
| 1 | john@example.com |
| 2 | bob@example.com |
| 3 | john@example.com |
+----+------------------+

+----+------------------+
| Id | Email      |
+----+------------------+
| 1 | john@example.com |
| 2 | bob@example.com |
+----+------------------+

delete from Person where Id not in (
	select t.min_id from (
		select min(Id) as min_id from Person group by Email
		) as t
	);

delete p1 from 
	Person as p1,Person as p2 
		where p1.Email=p2.Email and p1.Id > p2.Id;