你可以在MySQL数据表中设置指定的字段为 PRIMARY KEY（主键） 或者 UNIQUE（唯一） 索引来保证数据的唯一性。 让我们尝试一个实例：下表中无索引及主键，所以该表允许出现多条重复记录。CREATE TABLE person_tbl (first_name CHAR(20),last_name CHAR(20),sex CHAR(10) ); 如果你想设置表中字段first_name，last_name数据不能重复，你可以设置双主键模式来设置数据的唯一性， 如果你设置了双主键，那么那个键的默认值不能为NULL，...
id 姓名 课程名称 分数1 张三 数学 692 李四 数学 893 张三 数学 69删除除了自动编号不同,其他都相同的学生冗余信息 完整的sql语句如下：DELETE FROM tablename where id not in (select bid from (select min(id) as bid from tablename group by name,kecheng,fenshu) as b ) ;解释：select bid from (select min(id) as bid from tablename group by name,kec...
问：如何查询重复数据？ select name,sex,count(*) from test group by name,sex HAVING count(*)>1。 问：如何删除重复数据并保留ID最大的数据？ delete a from test a join (select name,sex,count(*) ,max(id) as id from test group by name,sex HAVING count(*)>1) b on a.name=b.name where a.id<b.idmysql如何删除重复数据并保留ID最大的数据标签：16px having group by name join style rom test from 本...
* FROMpeople WHEREpeopleId IN (SELECTpeopleIdFROMpeopleGROUP BYpeopleIdHAVINGcount(peopleId) > 1)1234567891011121314151234567891011121314152、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DELETEFROMpeople WHEREpeopleName IN (SELECTpeopleNameFROMpeopleGROUP BYpeopleNameHAVINGcount(peopleName) > 1) AND peopleId NOT IN (SELECTmin(peopleId)FROMpeopleGROUP BYpeo...
删除数据表的重复数据时，请先备份数据表。 方法一# 保留主键 ID 较小的那条记录 DELETE n1 FROM names n1, names n2 WHERE n1.id > n2.id AND n1.name = n2.name# 保留主键 ID 较大的那条记录 DELETE n1 FROM names n1, names n2 WHERE n1.id < n2.id AND n1.name = n2.name 方法二 参考链接：Delete all Duplicate Rows except for One in MySQL? [duplicate] MySQL 数据库删除表中重复数据标签：删除重复数据 exce flow ...
1. 问题描述 有时load或者insert操作导致 表数据有重复 2. 解决方案 通过临时表、主键id、倒腾去重 示例 2.1 create table student(name varchar(30) not null default ‘‘, age smallint(3) not null default 0,love varchar(50) not null default ‘‘ ) 插入一些数据......(包含重复) insert into student(name,age,love) values(‘zhangsan‘,15,‘basketball‘); insert into student(name,age,love) values...
FROM 表 WHERE id NOT IN ( SELECT id FROM ( SELECT min(b.id) AS id FROM 表 b GROUP BY b.重复字段 ) b ) Mysql 删除重复数据只保留id最小的标签：删除重复数据 重复数据 最小 重复 nbsp sql rom div sel 本文系统来源：http://www.cnblogs.com/blog5277/p/7605797.html
table tb002; create table tb002(id int primary key,c2 int,unique index uni_c2(c2)); begin; insert into tb002(id,c2) select 1,1; insert into tb002(id,c2) select 2,2; insert into tb002(id,c2) select 4,4; commit;假设有回话A和回话B,均使用REPEATABLE-READ隔离级别 ##========================================================## 首先回话A执行SQL：begin; select * from tb002;返回结果如下：##====================...
业务过程中，两张表求差 一开始一张小表，以为数据量不会很大，所以就没有做索引。当实际运行过程中，小表慢慢长大了，发现两张表求差的时间能达到几个小时！！！AMAZING！咋办，建索引呗然后问题出现了，小表有重复数据，咋整，一个一个删除太sb了写sqlDELETE FROM solr_indexed_max_incidentID WHERE incidentID IN (SELECT incidentID FROM solr_indexed_max_incidentID GROUP BY incidentID HAVING count(incidentID) > 1);报错...
统计重复数据出现次数 SELECT * FROM ( SELECT * FROM ( SELECT count(t1.compare_id) AS c1,t1.* FROM t1 LEFT JOIN t3 ON t1.compare_id=t3.compare_id WHERE t1.compare_id=t3.compare_id GROUP BY t1.compare_id ) t ) a1 LEFT JOIN ( SELECT * FROM ( SELECT count(t2.compare_id) AS c2,t2.* FROM t2 LEFT JOIN t3 ON t2.compare_id=t3.compar...
DELETE FROM `user` WHERE id NOT IN(SELECT * FROM(SELECT id FROM `user` GROUP BY username)AS b) 理解：先从里面的SQL开始看1、SELECT id FROM `user` GROUP BY username 根据名字分组查询出每组的ID。2、SELECT * FROM(SELECT id FROM `user` GROUP BY username) AS b 这句话中有2个疑问点， 第一、为什么要套这样一个select？因为 更新数据时使用了查询，而查询的数据又做更新的条件，mysql不支持这种方式 如果不套上...
120w数据删除了8w条，耗时1分24秒DELETE FROM table WHERE id NOT IN (SELECT * FROM (SELECT MAX(id) FROM table GROUP BY title) AS t);mysql 删除重复数据命令标签：mysq mys 重复 from title mysql sel group 除了 本文系统来源：https://www.cnblogs.com/yerkle/p/9813490.html
* FROM oa_user WHERE UserName IN (SELECT UserName FROM oa_user GROUP BY UserName HAVING COUNT(UserName) >1) ORDER BY UserNameoa_user表名，UserName需要查重复的字段名 mysql查询重复数据标签：mysql sel 数据 font username code order class sql 本文系统来源：https://www.cnblogs.com/penghq/p/9929094.html
mysql删除表中重复数据,mysql中是不能直接删除查询出来的记录的,需要使用一个临时表来解决,方式如下:delete from student where stId in(select stId from (select min(stId) stId from student group by stNo having count(stNo) >1) temp_user )如果有多条重复语句,那么重复执行以上语句即可,直到没有执行结果为止。 mysql删除重复数据标签：直接 pre group by sele 数据 重复执行 sql lock student 本文系统来...
表结构如下，需要增加xx，yy复合唯一索引。create table table_a (id int(11) NOT NULL AUTO_INCREMENT,xx int(11) NOT NULL,yy int(11) NOT NULL,PRIMARY KEY (id)) ENGINE=InnoDB DEFAULT CHARSET=utf8; 保留最小iddelete a.* from table_a as a,( select min(id) id , xx,yy from table_a group by xx,yy having count(1)>1) as b where a.yy=b.yy and a.xx=b.xx and a.id > b.id; 保留最大iddelete a.* from table_a as a,( ...