Question

我想选择未标记为用户阅读的所有帖子。

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

我想选择在此查询中未选择的所有数据

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

我希望输出像

post_id       post_message
2              good night
3              good morning
5              cool

Answer 1

您可以使用not in运算符：

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

如果您只想排除用户3已阅读的帖子，您可以在内部查询中添加where子句：

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

选择查询中不包含的数据

2 个答案: