MySQL中刪除重復數據只保留一條

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

 

 

用SQL語句,刪除掉重復項只保留一條

在幾千條記錄里,存在着些相同的記錄,如何能用SQL語句,刪除掉重復的呢 
1、查找表中多余的重復記錄，重復記錄是根據單個字段（peopleId）來判斷

用SQL語句,刪除掉重復項只保留一條

在幾千條記錄里,存在着些相同的記錄,如何能用SQL語句,刪除掉重復的呢 
1、查找表中多余的重復記錄，重復記錄是根據單個字段（peopleId）來判斷

SELECT * FROM people WHERE peopleId IN ( SELECT peopleId FROM people GROUP BY peopleId HAVING count(peopleId) > 1 )

 

2、刪除表中多余的重復記錄，重復記錄是根據單個字段（peopleId）來判斷，只留有rowid最小的記錄

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、查找表中多余的重復記錄（多個字段）

SELECT * FROM vitae a WHERE (a.peopleId, a.seq) IN ( SELECT peopleId, seq FROM vitae GROUP BY peopleId, seq HAVING count(*) > 1 )

4、刪除表中多余的重復記錄（多個字段），只留有rowid最小的記錄

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、查找表中多余的重復記錄（多個字段），不包含rowid最小的記錄

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.消除一個字段的左邊的第一位：

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

7.消除一個字段的右邊的第一位：

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

8.假刪除表中多余的重復記錄（多個字段），不包含rowid最小的記錄

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