--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)