MySQL中查询、删除重复记录的方法大全

MySQL 过滤重复数据 深知大多数初中级Java工程师,想要提升技能,往往是自己摸索成长或者是报班学习,但对于培训机构动则近万的学费,着实压力不小。自己不成体系的自学效果低效又漫长,而且极易碰到天花板技术停滞不前!因此收集整理了一份《Java开发全套学习资料》送给大家,初衷也很简单,就是希望能够帮助到想自学提升又不知道该从何学起的朋友,同时减轻大家的负担。 阅读详情

查找所有重复标题的记录:

select title,count(*) as count from user_table group by title having count>1;

SELECT * FROM t_info a WHERE ((SELECT COUNT(*) FROM t_info WHERE Title = a.Title) > 1) ORDER BY Title DESC

一、查找重复记录

1、查找全部重复记录

SELECT * FROM t_info a WHERE ((SELECT COUNT(*) FROM t_info WHERE Title = a.Title) > 1) ORDER BY Title DESC

2、过滤重复记录(只显示一条)

Select * From HZT Where ID In (Select Max(ID) From HZT Group By Title)

注:此处显示ID最大一条记录

二、删除重复记录

1、删除全部重复记录(慎用)

Delete 表 Where 重复字段 In (Select 重复字段 From 表 Group By 重复字段 Having Coun 《一线大厂Java面试题解析+后端开发学习笔记+最新架构讲解视频+实战项目源码讲义》无偿开源 威信搜索公众号【编程进阶路】 t(*)>1)

2、保留一条(这个应该是大多数人所需要的 _)

Delete HZT Where ID Not In (Select Max(ID) From HZT Group By Title)

**注:**此处保留ID最大一条记录

三、举例

1、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

select * from people where peopleId in (select peopleId from people group by peopleId having count(peopleId) > 1)

2、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

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)

3、查找表中多余的重复记录(多个字段)

select * from vitae a where (a.peopleId,a.seq) in (select peopleId,seq from vitae group by peopleId,seq having count(*) > 1)

4、删除表中多余的重复记录(多个字段),只留有rowid最小的记录

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)

MySQL 数据库中如何高效删除重复数据 重复数据在数据库中可能是一个常见的问题,它会增加存储空间的使用,降低查询性能,并且可能导致数据不一致性。这种方法使用临时表来存储去重后的数据,并在重命名表的过程中交换表的名称。这种方法通过使用子查询和临时表,找到重复数据的主键,并删除这些主键所对应的数据。步骤1:创建一个临时表,该表具有与原始表相同的结构。步骤1:创建一个临时表,存储要删除的重复数据的主键。步骤1:创建一个临时表,存储要删除的重复数据的主键。步骤3:重命名原始表,并将临时表重命名为原始表。步骤3:删除临时表。步骤3:删除临时表。 阅读详情

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