Sql 如何将子查询的结果与另一个表联接？

。试图将借阅者、书籍和作者的结果联系起来

预期结果：

AUTHORID         AUTHORFIRSTNAME      AUTHORLASTNAME
1                     JIM                   SPARKS
2                     JAMES                 ALLEN
3                     MARCUS                RASHFORD
20                    PAUL                  POGBA
22                    THIERRY               HENRY

---

但我不确定如何链接返回的顶级authorids以检索authorfirstname和lastname，但我没有在子查询中提到author表，因此，如果我正确获得它，您希望执行以下操作：

select authorid, authorfirstname, authorlastname 
 from 
  (select a.authorid, a.authorfirstname, a.authorlastname 
   from author a, borrower b, book c 
   where a.authorid = c.authorid and c.bookid = b.bookid
   and b.borrowdate like '%2017' 
    group by c.bookauthor 
    order by count(*) desc) xx 
 where rownum <=5

---

您可以将这三个表与秩分析函数按降序联接，以便在子查询中计数，然后在主查询中取小于等于5的值：

SELECT authorid, authorfirstname, authorlastname
  FROM
  (
  SELECT a.authorid, a.authorfirstname, a.authorlastname, 
         rank() over (order by count(*) desc)  as rnk
    FROM AUTHOR a
    LEFT JOIN BOOK bk ON a.authorid = bk.authorid
    LEFT JOIN BORROWER br ON br.bookid = bk.bookid
   WHERE br.borrowdate between date'2017-01-01' and date'2017-12-31'
   GROUP BY a.authorid, a.authorfirstname, a.authorlastname
   )
  WHERE rnk <= 5
  ORDER BY rnk

其中，我在日期“2017-01-01”和日期“2017-12-31”之间使用了br.borrowdate，而不是像“%2017”这样的charbr.borrowdate，以便能够受益于borrowdate列上的索引（如果存在）

上面的这些查询返回的行是有联系的，例如，如果多行与第5行的值匹配，则它们会带来多于5行的行

---

不要使用rownum伪列进行排名，因为它的值是在排序之前计算的，可能会产生错误的结果。

示例数据和期望的结果会使问题更容易理解。什么是borrowdate列的数据类型：是日期还是某种字符串？borrowdate的格式为字符串类型-varchar2@GordonLinoff干杯-我试图让我的这个问题更容易理解。感谢你的反馈哦，天哪！对类似于此，但不确定如何格式化以显示结果。这比我想象的要整洁得多！一直在试图搞乱，但可能SQL还是太差了。吼叫声谢谢你的帮助

SELECT a.authorid, a.authorfirstname, a.authorlastname, 
       rank() over (order by count(*) desc)  as rnk
  FROM AUTHOR a
  LEFT JOIN BOOK bk ON a.authorid = bk.authorid
  LEFT JOIN BORROWER br ON br.bookid = bk.bookid
 WHERE br.borrowdate between date'2017-01-01' and date'2017-12-31'
 GROUP BY a.authorid, a.authorfirstname, a.authorlastname
 ORDER BY rnk 
 FETCH FIRST 5 ROWS WITH TIES