Mysql 选择不在查询中的数据

我想选择所有未标记为已被用户阅读的帖子

tbl_邮政

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

待阅读时标记

user_id      post_id
3             1
3             4

我想选择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

我希望输出像这样

post_id       post_message
2              good night
3              good morning
5              cool

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);

如果只想排除用户3已阅读的帖子，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);

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);

如果只想排除用户3已阅读的帖子，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);

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

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

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这就是我要找的问题，谢谢兄弟。这就是我要找的问题，谢谢兄弟。