帖子有很多评论。评论(content,author_id)由用户创作。
如何检索给定用户(author_id = 1)尚未评论的博客帖子?
感谢。
答案 0 :(得分:0)
SELECT p.*
FROM post p
WHERE NOT EXISTS(SELECT 1
FROM comment c
WHERE c.post_id = p.post_id
AND c.author_id = 1)
您也可以使用LEFT JOIN执行此操作:
SELECT p.*
FROM post p
LEFT JOIN comment c
ON p.post_id = c.post_id
AND c.author_id = 1
WHERE c.post_id IS NULL
答案 1 :(得分:0)
在常规'ole SQL中,这看起来像这样:
SELECT post_id
FROM posts p
WHERE NOT EXISTS (
SELECT 1
FROM comments c
WHERE p.post_id = c.post_id
AND c.author_id = 1
)
我不确定如何使用Ruby on Rails / ActiveRecord语法执行此操作。