SELECT distinct QUESTIONID from kbox_base_relate_paperquestion UNION SELECT distinct QUESTIONID from kbox_base_relate_knowledgequestion UNION all SELECT distinct QUESTIONID from kbox_base_relate_courseassistquestion是正确的,但是在这个基础之上再加上select questionID from 之后就出错了。。请问是为什么啊?select * from (SELECT distinct QUESTIONID from kbox_base_relate_paperquestion UNION SELECT distinct QUESTIONID from kbox_base_relate_knowledgequestion UNION all SELECT distinct QUESTIONID from kbox_base_relate_courseassistquestion) 会 Every derived table must have its own alias的错误。请问是为什么啊?
(
SELECT distinct QUESTIONID from kbox_base_relate_paperquestion
UNION all
SELECT distinct QUESTIONID from kbox_base_relate_knowledgequestion
UNION all
SELECT distinct QUESTIONID from kbox_base_relate_courseassistquestion
) AS T
SELECT distinct QUESTIONID from kbox_base_relate_paperquestion UNION
SELECT distinct QUESTIONID from kbox_base_relate_knowledgequestion UNION all
SELECT distinct QUESTIONID from kbox_base_relate_courseassistquestion上面的查询语句是查出三张表中QUESTIONID 一列的值
select * from 后面应该是一张表
所以应该将以上语句封装成一张表
例如:select * from
(
SELECT distinct QUESTIONID from kbox_base_relate_paperquestion UNION
SELECT distinct QUESTIONID from kbox_base_relate_knowledgequestion UNION all
SELECT distinct QUESTIONID from kbox_base_relate_courseassistquestion
) A
select * from (select 'a' from dual) t