删除加入MySQL

Question

这是创建表的脚本:

CREATE TABLE clients (
   client_i INT(11),
   PRIMARY KEY (client_id)
);
CREATE TABLE projects (
   project_id INT(11) UNSIGNED,
   client_id INT(11) UNSIGNED,
   PRIMARY KEY (project_id)
);
CREATE TABLE posts (
   post_id INT(11) UNSIGNED,
   project_id INT(11) UNSIGNED,
   PRIMARY KEY (post_id)
);

在我的PHP代码中,删除客户端时,我想删除所有项目帖子:

DELETE 
FROM posts
INNER JOIN projects ON projects.project_id = posts.project_id
WHERE projects.client_id = :client_id;

该职位表没有外键client_id,唯一的project_id.我想删除已通过的项目中的帖子client_id.

现在这不起作用,因为没有删除任何帖子.

Answer 1

您只需指定要从posts表中删除条目:

DELETE posts
FROM posts
INNER JOIN projects ON projects.project_id = posts.project_id
WHERE projects.client_id = :client_id

编辑:有关更多信息,您可以看到这个替代答案

Answer 2

由于您要选择多个表,因此要删除的表不再明确.你需要选择:

DELETE posts FROM posts
INNER JOIN projects ON projects.project_id = posts.project_id
WHERE projects.client_id = :client_id

在这种情况下,table_name1并且table_name2是相同的表,所以这将工作:

DELETE projects FROM posts INNER JOIN [...]

如果您想要,您甚至可以从两个表中删除:

DELETE posts, projects FROM posts INNER JOIN [...]

请注意,order by并且limit 不适用于多表删除.

另请注意,如果声明表的别名,则在引用表时必须使用别名:

DELETE p FROM posts as p INNER JOIN [...]

^{来自Carpetsmoker等的贡献.}

Answer 3

或者同样的事情,略有不同(IMO友好)的语法:

DELETE FROM posts 
USING posts, projects 
WHERE projects.project_id = posts.project_id AND projects.client_id = :client_id;

顺便说一句,使用连接的mysql几乎总是比子查询更快...

Answer 4

您也可以像这样使用ALIAS它只是在我的数据库中使用它!t是需要删除的表格!

DELETE t FROM posts t
INNER JOIN projects p ON t.project_id = p.project_id
AND t.client_id = p.client_id

Answer 5

我更习惯于子查询解决方案,但我还没有在MySQL中尝试过:

DELETE  FROM posts
WHERE   project_id IN (
            SELECT  project_id
            FROM    projects
            WHERE   client_id = :client_id
        );

Answer 6

MySQL使用JOIN删除记录

通常在SELECT语句中使用INNER JOIN从表中选择具有其他表中相应记录的记录.我们还可以使用带有DELETE语句的INNER JOIN子句来删除表中的记录以及其他表中的相应记录,例如,要删除满足特定条件的T1和T2表中的记录,请使用以下语句:

DELETE T1, T2
FROM T1
INNER JOIN T2 ON T1.key = T2.key
WHERE condition

请注意,您将表名T1和T2放在DELETE和FROM之间.如果省略T1表,则DELETE语句仅删除T2表中的记录,如果省略T2表,则仅删除T1表中的记录.

连接条件T1.key = T2.key指定T2表中需要删除的相应记录.

WHERE子句中的条件指定需要删除T1和T2中的哪些记录.

Answer 7

单表删除:

要从posts表中删除条目:

DELETE ps 
FROM clients C 
INNER JOIN projects pj ON C.client_id = pj.client_id
INNER JOIN posts ps ON pj.project_id = ps.project_id
WHERE C.client_id = :client_id;

要从projects表中删除条目:

DELETE pj 
FROM clients C 
INNER JOIN projects pj ON C.client_id = pj.client_id
INNER JOIN posts ps ON pj.project_id = ps.project_id
WHERE C.client_id = :client_id;

要从clients表中删除条目:

DELETE C
FROM clients C 
INNER JOIN projects pj ON C.client_id = pj.client_id
INNER JOIN posts ps ON pj.project_id = ps.project_id
WHERE C.client_id = :client_id;

多个表删除:

要从联接结果中删除多个表中的条目,您需要在DELETE逗号分隔列表后指定表名:

假设你想从所有三个表(删除条目posts,projects,clients)为特定的客户端:

DELETE C,pj,ps 
FROM clients C 
INNER JOIN projects pj ON C.client_id = pj.client_id
INNER JOIN posts ps ON pj.project_id = ps.project_id
WHERE C.client_id = :client_id

Answer 8

尝试如下:

DELETE posts.*,projects.* 
FROM posts
INNER JOIN projects ON projects.project_id = posts.project_id
WHERE projects.client_id = :client_id;