从两个标签中选择发布（AND）

Question

标签

tag_id      tag          post_id 
--------------------------------
1           category1    1
2           category2    1
3           etc          2
4           category3    1

交

post_id title
-------------
1       title1

我们如何获得title1，因为它位于category1＆amp;＆amp; category2

类似

SELECT TITLE 
  FROM post, tag 
 WHERE tag.post_id = post.post_id 
   AND tags.tag = 'category1','category2'

Answer 1

为了检查标题是否包含'category1'和'category2'，您可以使用以下SQL查询：

SELECT title 
FROM post 
JOIN tag ON post.post_id = tag.post_id 
WHERE tag.tag_id IN (SELECT tag_id FROM tag WHERE tag = 'category1')
AND tag.tag = 'category2';

要检查其他类别，只需重复WHERE子句：

SELECT title 
FROM post 
JOIN tag ON post.post_id = tag.post_id 
WHERE tag.tag_id IN (SELECT tag_id FROM tag WHERE tag = 'category1')
AND tag.tag_id IN (SELECT tag_id FROM tag WHERE tag = 'category2')
AND tag.tag = 'category3';

这将返回包含所有3个类别的标题的结果。

Answer 2

您可以像这样加入两个表：

SELECT post.* 
FROM post 
LEFT JOIN tag
ON post.post_id = tag.post_id
WHERE tag.tag IN ('category1','category2')
GROUP BY post.post_id
HAVING COUNT(post.post_id) >1;

See this SQLFiddle

注意：如果我们不使用HAVING子句，它也会返回任何单个值存在的记录

See this SQLFiddle

See the similar requirement with similar table structure.