考察字符串的处理
concat连接 以及group_concat的连接
with t as(
select distinct post_id,topic_id from Keywords,Posts
where locate(concat(' ',word,' '),concat(' ',content,' '))>0)
select post_id, group_concat(topic_id order by topic_id,'') topic from t group by post_id
union
select P.post_id,'Ambiguous!' from Posts P left join t on P.post_id = t.post_id
group by P.post_id having count(t.topic_id)=0