刚开始,根据我的想法,这个很简单嘛,上sql语句
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1 | delete from zqzrdp where tel in ( select min (dpxx_id) from zqzrdp group by tel having count (tel)>1); |
执行,报错!!~!~
异常意为:你不能指定目标表的更新在FROM子句。傻了,MySQL 这样写,不行,让人郁闷。
难倒只能分步操作,蛋疼
以下是网友写的,同样是坑爹的代码,我机器上运行不了。
1. 查询需要删除的记录,会保留一条记录。
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1 | 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。
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1 | 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
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1 | 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
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1 | 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
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1 | 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) |
看来想偷懒使用一句命令完成这个事好像不太显示,还是老老实实的分步处理吧,思路先建立复制一个临时表,然后对比临时表内的数据,删除主表里的数据
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123456789 | alter table tableName add autoID int auto_increment not null ; create table tmp select min (autoID) as autoID from tableName group by Name ,Address; create table tmp2 select tableName.* from tableName,tmp where tableName.autoID = tmp.autoID; drop table tableName; rename table tmp2 to tableName; |
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