--测试数据

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create table test as select * from dba_objects;

insert into test select * from test;

--查看是否有重复数据

select * from test order by object_id;

--用rowid删除

select rowid,a.* from test a order by object_id;

--根据rowid分组

--办法（1）not in

DELETE FROM test WHERE ROWID NOT IN (SELECT MAX(ROWID) FROM test GROUP BY object_id)

--办法（2) in

DELETE FROM test a

 WHERE ROWID IN (SELECT ROWID

                   FROM (SELECT row_number() over(PARTITION BY object_id ORDER BY ROWID) rn,

                                a.*

                           FROM test a)

                  WHERE rn > 1)

--办法3 exists

DELETE FROM test a

 WHERE EXISTS (SELECT NULL

          FROM test b

         WHERE a.object_id = b.object_id

           AND a.rowid < b.rowid)

--in的等价写法

DELETE FROM test a

 WHERE object_id IN (SELECT object_id

                       FROM test b

                      WHERE a.object_id = b.object_id

                        AND a.rowid < b.rowid)

--如果要保留3条重复数据

DELETE FROM test a

 WHERE ROWID IN (SELECT ROWID

                   FROM (SELECT row_number() over(PARTITION BY object_id ORDER BY ROWID) rn,

                                a.*

                           FROM test a)

                  WHERE rn > 3)

                  

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