这是我一直在努力解决的问题。 我需要从特定博客ID中提取所有帖子。另外,我需要提取属于每个帖子的所有标签。
问题是当帖子没有标签时,查询不会返回它。如何为标签单元格获取空结果而不是不对该行进行重新定位?
我有以下表格
帖子:
ID title
74 HELLO
75 HELLO2
76 HELLO3
tags_relation:
ID|post_id|tag_id
57 74 3
56 74 61
58 75 62
59 75 63
标记:
ID tag
3 Love
61 Sometag
62 Sometag1
63 Sometag2
64 Sometag3
65 Sometag4
这是我的疑问:
SELECT post . * ,
user.username,
user.picture,
GROUP_CONCAT(tag.tag SEPARATOR ',') AS tags
FROM `posts` AS post
INNER JOIN `users` AS USER ON USER.blog_id = post.blog_id
INNER JOIN `tags_relation` AS tags_relation
INNER JOIN `tags` AS tag ON tag.ID = tags_relation.tag_id
WHERE post.blog_id =1
AND post.status = 'publish'
AND post.ID = tags_relation.post_id
GROUP BY post.ID
ORDER BY post.timestamp DESC LIMIT 0,10;
答案 0 :(得分:10)
试试这个:
SELECT p.* ,
u.username,
u.picture,
GROUP_CONCAT(t.tag SEPARATOR ',') AS tags
FROM `posts` AS p
INNER JOIN `users` AS u ON u.blog_id = p.blog_id
LEFT JOIN `tags_relation` AS tr ON p.ID = tr.post_id
LEFT JOIN `tags` AS t ON t.ID = tr.tag_id
WHERE p.blog_id =1
AND p.status = 'publish'
GROUP BY p.ID
ORDER BY p.timestamp DESC LIMIT 0,10;