如何删除数据库表中相同记录

 如何删除表中相同的记录（比如相同的id，假设没有主键）

--方法1 

DELETE FROM EMP
WHERE ROWID NOT IN(SELECT MAX(ROWID) FROM EMP GROUP BY EMPNO)
--方法2

DELETE FROM emp e
WHERE ROWID NOT IN ( SELECT MIN(ROWID) FROM emp a
WHERE e.empno=a.empno);
--方法3

DELETE FROM table_name A
WHERE ROWID > ( SELECT min(ROWID) FROM table_name B WHERE A.col = B.col);