不管有没有数据，都不能使用在线重定义功能将VARCHR2字段修改成CLOB字段，已实测

--原表
CREATE TABLE table_o (ID NUMBER PRIMARY KEY, TIME varchar2(20)) 
;
--新表，改成clob类型 
CREATE TABLE table_n (ID NUMBER PRIMARY KEY, TIME clob) 
;
--校验是否可以重定义
begin
DBMS_REDEFINITION.CAN_REDEF_TABLE(USER, 'table_o', DBMS_REDEFINITION.CONS_USE_PK);
end;
/

--开始重定义 
begin
sys.DBMS_REDEFINITION.START_REDEF_TABLE(USER,
'table_o',
'table_n');
end;
/



ORA-42016: shape of interim table does not match specified column mapping
ORA-06512: at "SYS.DBMS_REDEFINITION", line 119
ORA-06512: at "SYS.DBMS_REDEFINITION", line 4692
ORA-06512: at "SYS.DBMS_REDEFINITION", line 6159
ORA-06512: at line 2