mysql删除重复数据记录sql语句总结

时间：2013-06-03 编辑：简简单单来源：一聚教程网

我最常用的方法是

代码如下	复制代码
//删除id重复的数据，适合id是手工主键 delete person as a from person as a, ( select *,min(id) from person group by id having count(1) > 1 ) as b where a.id = b.id

//查找重复的，并且除掉最小的那个

代码如下	复制代码
delete tb_person as a from tb_person as a, ( select *,min(id) from tb_person group by name having count(1) > 1 ) as b where a.name = b.name and a.id > b.id;

好了下面再总结一些

1. 查询需要删除的记录，会保留一条记录。

代码如下	复制代码
select a.id,a.subject,a.RECEIVER from test1 a left join (select c.subject,c.RECEIVER ,max(c.id) as bid from test1 c where status=0 GROUP BY RECEIVER,SUBJECT having count(1) >1) b on a.id< b.bid where a.subject=b.subject and a.RECEIVER = b.RECEIVER and a.id < b.bid

2. 删除重复记录，只保留一条记录。注意，subject,RECEIVER 要索引，否则会很慢的。

代码如下	复制代码
delete a from test1 a, (select c.subject,c.RECEIVER ,max(c.id) as bid from test1 c where status=0 GROUP BY RECEIVER,SUBJECT having count(1) >1) b where a.subject=b.subject and a.RECEIVER = b.RECEIVER and a.id < b.bid;

3. 查找表中多余的重复记录，重复记录是根据单个字段（peopleId）来判断

代码如下	复制代码
select * from people where peopleId in (select peopleId from people group by peopleId having count(peopleId) > 1)

4. 删除表中多余的重复记录，重复记录是根据单个字段（peopleId）来判断，只留有rowid最小的记录

代码如下	复制代码
delete from people where peopleId in (select peopleId from people group by peopleId having count(peopleId) > 1) and rowid not in (select min(rowid) from people group by peopleId having count(peopleId )>1)

5.删除表中多余的重复记录（多个字段），只留有rowid最小的记录

代码如下	复制代码
delete from vitae a where (a.peopleId,a.seq) in (select peopleId,seq from vitae group by peopleId,seq having count() > 1) and rowid not in (select min(rowid) from vitae group by peopleId,seq having count()>1)

说了这么多了我们来个例子吧

例子如下:

代码如下

复制代码

drop table t_user;
create table t_user(
id int(5) not null auto_increment,
username varchar(10),
age int(3),
primary key(id)
);

insert into t_user(username,age) values('aaa',20);
insert into t_user(username,age) values('aaa',20);
insert into t_user(username,age) values('bbb',20);
insert into t_user(username,age) values('bbb',20);
insert into t_user(username,age) values('ccc',20);
insert into t_user(username,age) values('ccc',20);
insert into t_user(username,age) values('ddd',20);
insert into t_user(username,age) values('ddd',20);

mysql> select * from t_user;
+----+----------+------+
| id | username | age |
+----+----------+------+
| 1 | aaa      |   20 |
| 2 | aaa      |   20 |
| 3 | bbb      |   20 |
| 4 | bbb      |   20 |
| 5 | ccc      |   20 |
| 6 | ccc      |   20 |
| 7 | ddd      |   20 |
| 8 | ddd      |   20 |
+----+----------+------+

mysql> delete t_user from t_user , (select id from t_user group by username having count(*)>1 ) as t2 where t_user.id=t2.id;
Query OK, 4 rows affected (0.05 sec)

mysql> select * from t_user;
+----+----------+------+
| id | username | age |
+----+----------+------+
| 2 | aaa      |   20 |
| 4 | bbb      |   20 |
| 6 | ccc      |   20 |
| 8 | ddd      |   20 |
+----+----------+------+

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