oracle删除一个表中的重复数据，且只保留一条

 创建表：

-- Create table
create table STUDENT
(
  ID   INTEGER,
  语文 VARCHAR2(4000),
  数学 VARCHAR2(50),
  英语 VARCHAR2(50)
)
tablespace USERS
  pctfree 10
  initrans 1
  maxtrans 255
  storage
  (
    initial 64K
    next 1M
    minextents 1
    maxextents unlimited
  );

插入数据：

insert into student(id) values('1');
insert into student(id) values('1');
insert into student(id) values('1');
insert into student(id) values('1')

例子1：查找一个表中的重复数据，重复记录是根据单个字段（Id）来判断，表名为STUDENT

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

例子2：删除表中多余的重复记录，重复记录是根据单个字段（Id）来判断，只留有rowid最小的记录，表名为STUDENT

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)