一个选择是只改变表。
下面是一个例子：
具有long数据类型列的表：

SQL> create table test (col long);

Table created.

让我们填充它：

SQL> begin
  2    for cur_r in (select text from all_views
  3                  where text_length < 30000
  4                    and text is not null
  5                 )
  6    loop
  7      insert into test (col) values (cur_r.text);
  8    end loop;
  9  end;
 10  /

PL/SQL procedure successfully completed.

它包含多少行？

SQL> select count(*) from test;

  COUNT(*)
----------
        45

只是一个摘录：

SQL> select * from test where rownum = 1;

COL
--------------------------------------------------------------------------------
SELECT  q_name QUEUE, qt.msgid MSG_ID, corrid CORR_ID,  priority MSG_PRIORITY,

OK，现在alter table修改long为clob：

SQL> alter table test modify col clob;

Table altered.

结果：

SQL> select * from test where rownum = 1;

COL
--------------------------------------------------------------------------------
SELECT  q_name QUEUE, qt.msgid MSG_ID, corrid CORR_ID,  priority MSG_PRIORITY,

SQL>