Question

我有一个标准的文章，标签和tag_map表。我SELECT作者用单个标签作为

SELECT author_id, COUNT(*) AS author_articles FROM articles a 
JOIN tag_map b ON a.article_id=b.article_id
JOIN tags c ON b.tag_id=c.tag_id AND c.tag='tag1'
JOIN author_map d ON a.article_id=d.article_id
JOIN authors e ON d.author_id=e.author_id
GROUP BY e.author_id

但我如何SELECT有两个或多个标签的文章？

Answer 1

一些简单的方法。

加入，但标签是必需的标签之一。计算DISTINCT文章（否则计数将加倍），但使用HAVING子句检查文章是否有2个标签。

SELECT author_id, 
        COUNT(DISTINCT a.article_id) AS author_articles 
FROM articles a 
JOIN tag_map b ON a.article_id=b.article_id
JOIN tags c ON b.tag_id = c.tag_id AND c.tag IN ('tag1', 'tag2')
JOIN author_map d ON a.article_id=d.article_id
JOIN authors e ON d.author_id=e.author_id
GROUP BY e.author_id
HAVING COUNT(DISTINCT c.tag_id) = 2

或者你可以做一个额外的加入。

SELECT author_id, 
        COUNT(*) AS author_articles 
FROM articles a 
JOIN tag_map b ON a.article_id=b.article_id
JOIN tags c1 ON b.tag_id = c1.tag_id AND c1.tag = 'tag1'
JOIN tags c2 ON b.tag_id = c2.tag_id AND c2.tag = 'tag2'
JOIN author_map d ON a.article_id=d.article_id
JOIN authors e ON d.author_id=e.author_id
GROUP BY e.author_id

Answer 2

您需要在Count子句中使用条件HAVING。试试这个：

SELECT author_id, COUNT(*) AS author_articles FROM articles a 
  JOIN tag_map b ON a.article_id=b.article_id
  JOIN tags c ON b.tag_id=c.tag_id
  JOIN author_map d ON a.article_id=d.article_id
  JOIN authors e ON d.author_id=e.author_id
GROUP BY e.author_id
HAVING COUNT(c.tag_id)>1

Answer 3

在count()

中使用条件having

如果您可以使用重复的标签

 HAVING COUNT(CASE WHEN c.tag ='tag1' THEN 1 END) >= 1
    AND COUNT(CASE WHEN c.tag ='tag2' THEN 1 END) >= 1

如果标签是唯一的，您可以简化为

 HAVING COUNT(CASE WHEN c.tag IN ('tag1', 'tag2') THEN 1 END) = 2

如何将表连接到具有多个标签的SELECT文章？

3 个答案: