The method of removing duplicate data in mysql Database

This article mainly introduces the mysql database to remove duplicate data methods, with a certain reference value, friends can refer to the need. I hope you all have a lot of success after reading this article. Let's take a look at it together.

mysql database to remove duplicate data method: 1. Query the records to be deleted, will retain a record;2. Delete duplicate records, only retain a record, code is [delete a from test1 a, (...) as bid from test1 c where..】。

How to remove duplicate data from mysql database:

1. Query the records to be deleted, and one record will be retained.

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

1)

4. Delete redundant duplicate records in the table. Duplicate records are judged according to a single field (peopleId), leaving only records with the smallest rowid.

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)

Delete redundant duplicate records (multiple fields) in the table, leaving only records with the smallest rowid

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)

It seems that it is not obvious to be lazy to use a command to complete this matter. It is better to handle it step by step honestly. The idea is to create and copy a temporary table first, then compare the data in the temporary table and delete the data in the main table.

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; Thank you for reading this article carefully. I hope that Xiaobian will share the method content of removing duplicate data in mysql database to help everyone. At the same time, I hope that everyone will support it more. Pay attention to the industry information channel. If you encounter problems, find them. Detailed solutions are waiting for you to learn!