mysql如何去掉数据库中重复记录

1. 查询需要删除的记录，会保留一条记录。

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。

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

思路：数据库如果存在就更新，不存在就插入

首先：1.对你要设置的表，点击右键--管理索引--新建--选择要唯一的主键--在“索引选项”中选择“唯一性”--应用

思路：数据库如果存在就更新，不存在就插入

1.对你要设置的表，点击右键--管理索引--新建--选择要唯一的主键--在“索引选项”中选择“唯一性”--应用

2、语句：INSERT INTO 表名(字段,字段,字段,字段) VALUES ('127.0.0.5','1',NOW(),NOW())

ON DUPLICATE KEY UPDATE 字段 = online_num+1,last_time = NOW()

自己延伸一下就明白了

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