orcale 列改为大字段

--添加临时列
ALTER TABLE MPD_TASK_LIST ADD(
  CLOB_TEMP clob
);
--数据拷贝到临时列
update MPD_TASK_LIST set CLOB_TEMP = MPD_PREPARATION;
--数据设置为null
update MPD_TASK_LIST set MPD_PREPARATION = null;
--修改数据类型
alter table MPD_TASK_LIST modify MPD_PREPARATION long;
alter table MPD_TASK_LIST modify MPD_PREPARATION clob;
--拷贝回来
update MPD_TASK_LIST set MPD_PREPARATION = CLOB_TEMP;
--删除临时列
alter table MPD_TASK_LIST drop column CLOB_TEMP;