做论坛类网站时，会遇到主题表和回复表的内容字段都为clob字段，此时要取出一个贴子时，会使用到union，它这时会报ORA-00932 不一致的数据类型 要求 -得到的却是clob错误。

原因是：lob字段不能做group by，而union中需要使用group by过滤到重复纪录，所以不行

解决方法：用union all就可以了

select title,
       content,
       writerid,
       writer,
       speechtime,
       points,
       faceid,
       point,
       gold,
       idiographp,
       idiographt
  from ((
  select
 
  title, content, writerid, writer, speechtime, points
           from vo_bbstopictab
          where topicid = '1153996430976t2cj0'
         
         
          ) union all
        (select title, content, writerid, writer, speechtime, points
           from vo_bbsreplytab
          where topicid = '1153996430976t2cj0')),
       vo_usertab
 where writerid = userid
 order by speechtime