Question

特别是，这些表格是：文章，作者，作者_文章（连接作者和文章），主题领域（作者的主题领域），以及authors_subjectareas（将作者连接到他们的主题领域）。

我希望逐行阅读文章表，找到每篇文章的作者，然后转到他们的主题领域，并计算该文章的所有共同作者的主题领域，最后分配主题领域。该文章的最大频率。我编写如下代码，但问题是它是针对所有文章而不是单独为每篇文章做的！

select art.name as title, art.theAbstract as abstract, sub.name as subjectArea
from
articles as art, authors as aut, subjectareas as sub, authors_articles as aa, 
authors_subjectareas as asub 
where
art.id = aa.article and aut.id = aa.author and asub.author = aut.id and
sub.id = asub.subjectArea and (art.year >= 2000 and art.year <= 2004)
group by subjectArea
Order by count(subjectArea) DESC
LIMIT 1

非常感谢您的评论......

Answer 1

您正在寻求从物化表中获取groupwise maximum：

SELECT t2.name AS title, t2.theAbstract AS abstract, sub.name AS subjectArea
FROM (

  -- get each article's maximum co-author subject frequency
  SELECT art.id, MAX(freq) freq FROM (

    -- the subject frequencies of each article
    SELECT   art.id, COUNT(*) freq
    FROM     authors_articles aa
        JOIN authors_subjectareas asub USING (author)
        JOIN articles art ON art.id = aa.article
    GROUP BY art.id, asub.subjectArea

  ) t

) t1 NATURAL JOIN (

  -- the information we actually want
  SELECT   art.id, art.name, art.theAbstract, asub.subjectArea, COUNT(*) freq
  FROM     authors_articles aa
      JOIN authors_subjectareas asub USING (author)
      JOIN articles art ON art.id = aa.article
  GROUP BY art.id, asub.subjectArea

) t2 JOIN subjectareas sub ON sub.id = t2.subjectArea

如何从联合表中选择具有最大频率的行？

1 个答案: