选择不在查询中的数据

Question

我想选择所有未被用户标记为已读的帖子。

tbl_post

post_id post_message 
1   hello world 
2   good night 
3   good morning 
4   incredible 
5   cool 

tbl_mark_as_read

user_id  post_id 
3    1 
3    4 

我要选择不会在此查询

SELECT p.post_id,p.post_message FROM tbl_post AS p 
LEFT JOIN tbl_mark_as_read AS r 
ON r.post_id = p.post_id 
AND r.user_id = 3 

我想选择的所有数据输出到像

post_id  post_message 
2    good night 
3    good morning 
5    cool 

Answer 1

您可以使用not in操作：

SELECT * 
FROM tbl_post 
WHERE post_in NOT IN (SELECT post_id FROM tbl_mark_as_read); 

如果你想给该用户3已经阅读仅仅排除的职位，你可以添加一个where子句内查询：

SELECT * 
FROM tbl_post 
WHERE post_in NOT IN (SELECT post_id 
         FROM tbl_mark_as_read 
         WHERE user_id = 3); 

Answer 2

试试这个：

SELECT p.post_id,p.post_message FROM tbl_post AS p 
LEFT JOIN tbl_mark_as_read AS r 
ON r.post_id = p.post_id 
AND r.user_id = 3 
where r is null