MySQL中删除重复数据只保留一条

转自：https://blog.csdn.net/u014723529/article/details/51218638

 

 

用SQL语句,删除掉重复项只保留一条

在几千条记录里,存在着些相同的记录,如何能用SQL语句,删除掉重复的呢 
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

用SQL语句,删除掉重复项只保留一条

在几千条记录里,存在着些相同的记录,如何能用SQL语句,删除掉重复的呢 
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 peopleName IN ( SELECT peopleName FROM people GROUP BY peopleName HAVING count(peopleName) > 1 ) AND peopleId NOT IN ( SELECT min(peopleId) FROM people GROUP BY peopleName HAVING count(peopleName) > 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 )

5、查找表中多余的重复记录（多个字段），不包含rowid最小的记录

SELECT * 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 )

6.消除一个字段的左边的第一位：

UPDATE tableName SET [ Title ]= RIGHT ([ Title ],(len([ Title ]) - 1)) WHERE Title LIKE '村%'

7.消除一个字段的右边的第一位：

UPDATE tableName SET [ Title ]= LEFT ([ Title ],(len([ Title ]) - 1)) WHERE Title LIKE '%村'

8.假删除表中多余的重复记录（多个字段），不包含rowid最小的记录

UPDATE vitae SET ispass =- 1 WHERE peopleId IN ( SELECT peopleId FROM vitae GROUP BY peopleId