如何实现子查询以选择与三个主题中的两个主题匹配的行？

Posted 2021-05-07

我如何找到不带set运算符的完全覆盖三个不同SQL系统中的两个的书籍。我正在使用三个主题ID“ SSRV”，“ ORA”，“ mysql”，并且需要输出三个中的两个。例如，这本书可能有一个SSRV主题和一个ORA主题，但没有MySQL。这些主题的任何两个组合足以通过我们的过滤器。

我要显示符合此测试的book_id和书名。

  SELECT book_id
       , title
    FROM a_bkinfo.books B
   WHERE book_id IN (
       SELECT book_id
         FROM a_bkinfo.book_topics BT
    WHERE topic_id = 'SSRV' )
  AND book_id IN (
       SELECT book_id
         FROM a_bkinfo.book_topics BT
    WHERE topic_id = 'ORA' )
  AND book_id IN (
       SELECT book_id
         FROM a_bkinfo.book_topics BT
    WHERE topic_id = 'MySQL' )
  AND book_id IN (
        SELECT COUNT(*) 
                   FROM (  
                       SELECT book_id
                           ,  count(topic_id) AS topics
                         FROM a_bkinfo.book_topics BT 
                        GROUP BY book_id
                        HAVING count(topic_id) = 2
                        ) t 
              ;  

更新版本：

   SELECT book_id
 , title
 FROM a_bkinfo.books B
 WHERE book_id IN (
       SELECT book_id
         FROM a_bkinfo.book_topics BT
    WHERE topic_id ='SSRV'
        OR topic_id ='ORA' )
AND book_id IN (
        SELECT book_id
          FROM a_bkinfo.book_topics BT
    WHERE topic_id ='SSRV' 
        OR topic_id ='MySQL')
AND book_id IN (
        SELECT book_id
          FROM a_bkinfo.book_topics BT
    WHERE topic_id ='ORA' 
        OR topic_id ='MySQL');

答案

SELECT b.book_id, b.title, COUNT(*) FROM books b
INNER JOIN book_topics bt ON (b.book_id = bt.book_id)
GROUP BY b.book_id, b.title
HAVING COUNT(*) = 2

如果在book_topics中每个书-主题关系只有一行，这将起作用。这些对也必须是唯一的。如果您的数据不符合要求，则需要更复杂的查询。更新因为book_id是唯一的标识符，所以新版本是：

SELECT b.book_id FROM books b
INNER JOIN book_topics bt ON (b.book_id = bt.book_id)
GROUP BY b.book_id
HAVING COUNT(topic_id) = 2
要求与上述相同。