mysql - 构建包含映射表的查询？

Question

我正在构建一个非常简单的cms。
其中的两个对象是文章和标签这是我当前拥有的数据库架构:

使用这个我可以按标签获取文章列表SELECT ... WHERE web_tag.Name = 'News'

<小时/>

问题

如何获取不包含标签的文章列表。

我尝试做

SELECT ... WHERE web_tag.Name != 'News'

如果文章只有一个标签，则此方法有效。如果文章明显有多个标签，则不起作用

非常感谢!

Answer 1

一种方法

SELECT a.id_article, a.name
  FROM web_article a
 WHERE NOT EXISTS
(
  SELECT *
    FROM web_tag_to_article ta JOIN web_tag t
      ON ta.id_tag = t.id_tag
   WHERE id_article = a.id_article
     AND t.name = 'News'
)

或

SELECT id_article, name
  FROM web_article
 WHERE id_article NOT IN
(
  SELECT id_article
    FROM web_tag_to_article ta JOIN web_tag t
      ON ta.id_tag = t.id_tag
   GROUP BY id_article
  HAVING MAX(t.name = 'News') = 1
)

或

SELECT a.id_article, a.name
  FROM web_article a LEFT JOIN web_tag_to_article ta 
    ON a.id_article = ta.id_article LEFT JOIN web_tag t
    ON ta.id_tag = t.id_tag
 GROUP BY a.id_article, a.name
HAVING MAX(COALESCE(t.name,'') = 'News') = 0

这里是SQLFiddle 演示