筆記：Oracle查詢重覆數據並刪除，只保留一條記錄

1、查找表中多餘的重覆記錄，重覆記錄是根據單個欄位（Id）來判斷

select * from 表 where Id in (select Id from 表 group byId having count(Id) > 1)

2、刪除表中多餘的重覆記錄，重覆記錄是根據單個欄位（Id）來判斷，只留有rowid最小的記錄

DELETE from 表 WHERE (判斷欄位) IN ( SELECT 判斷欄位 FROM 表 GROUP BY 判斷欄位 HAVING COUNT(判斷欄位) > 1) AND ROWID NOT IN (SELECT MIN(ROWID) FROM 表 GROUP BY id HAVING COUNT(*) > 1);

註意：AND後面的句子獲取到的是除去擁有rowid最小的所有的記錄（單個不重覆記錄也包含），Where 與 AND之間是獲取所有含有重覆記錄的欄位。

3、查找表中多餘的重覆記錄（多個欄位）

select * from 表 a where (a.Id,a.seq) in(select Id,seq from 表 group by Id,seq having count(*) > 1)

4、刪除表中多餘的重覆記錄（多個欄位），只留有rowid最小的記錄（原理同2）

delete from 表 a where (a.Id,a.seq) in (select Id,seq from 表 group by Id,seq having count(*) > 1) and rowid not in (select min(rowid) from 表 group by Id,seq having count(*)>1)

示例二：delete from student where s_id not in(select min(s_id) from student group by s_name,c_id);

5、查找表中多餘的重覆記錄（多個欄位），不包含rowid最小的記錄

select * from 表 a where (a.Id,a.seq) in (select Id,seq from 表 group by Id,seq having count(*) > 1) and rowid not in (select min(rowid) from 表 group by Id,seq having count(*)>1)