oracle删除一个表中的重复数据，且只保留一条

       SELECT ID ,
              COUNT(1)
         FROM STUDENT T
     GROUP BY T.ID HAVING COUNT(ID) > 1

DELETE FROM STUDENT
      WHERE ID    IN     (SELECT ID 
                            FROM STUDENT T
                        GROUP BY T.ID HAVING COUNT(ID) > 1)
        AND ROWID NOT IN (SELECT MIN(ROWID)
                            FROM STUDENT T
                        GROUP BY T.ID
                          HAVING COUNT(T.ID) > 1)