在一个查询中从两个表中删除

我在 MySQL 中有两个表

#messages table  :
messageid
messagetitle
.
.


#usersmessages table
usersmessageid
messageid
userid
.
.

现在，如果我想从消息表中删除它就可以了。但是当我通过 messageid 删除消息时，用户消息上的记录仍然存在，我必须同时从这两个表中删除。

我使用了以下查询:

DELETE FROM messages LEFT JOIN usersmessages USING(messageid) WHERE messageid='1' ;

然后我测试

   DELETE FROM messages , usersmessages
WHERE messages.messageid = usersmessages.messageid
and messageid='1' ;

但是这两个查询并没有完成这个任务。

498437 次浏览
小开
最佳答案

Can't you just separate them by a semicolon?

Delete from messages where messageid = '1';
Delete from usersmessages where messageid = '1'

OR

Just use INNER JOIN as below

DELETE messages , usersmessages  FROM messages  INNER JOIN usersmessages
WHERE messages.messageid= usersmessages.messageid and messages.messageid = '1'
小开

You should either create a FOREIGN KEY with ON DELETE CASCADE:

ALTER TABLE usersmessages
ADD CONSTRAINT fk_usermessages_messageid
FOREIGN KEY (messageid)
REFERENCES messages (messageid)
ON DELETE CASCADE

, or do it using two queries in a transaction:

START TRANSACTION;;


DELETE
FROM    usermessages
WHERE   messageid = 1


DELETE
FROM    messages
WHERE   messageid = 1;


COMMIT;

Transaction affects only InnoDB tables, though.

小开

You have two options:

First, do two statements inside a transaction:

BEGIN;
DELETE FROM messages WHERE messageid = 1;
DELETE FROM usermessages WHERE messageid = 1;
COMMIT;

Or, you could have ON DELETE CASCADE set up with a foreign key. This is the better approach.

CREATE TABLE parent (
id INT NOT NULL,
PRIMARY KEY (id)
);


CREATE TABLE child (
id INT, parent_id INT,
FOREIGN KEY (parent_id) REFERENCES parent(id) ON DELETE CASCADE
);

You can read more about ON DELETE CASCADE here.

小开 
DELETE a.*, b.*
FROM messages a
LEFT JOIN usersmessages b
ON b.messageid = a.messageid
WHERE a.messageid = 1

translation: delete from table messages where messageid =1, if table uersmessages has messageid = messageid of table messages, delete that row of uersmessages table.

小开

Try this please 

DELETE FROM messages,usersmessages


USING messages


INNER JOIN usermessages on (messages.messageid = usersmessages.messageid)


WHERE messages.messsageid='1'
小开 
DELETE message.*, usersmessage.* from users, usersmessage WHERE message.messageid=usersmessage.messageid AND message.messageid='1'
小开

no need for JOINS: 

DELETE m, um FROM messages m, usersmessages um


WHERE m.messageid = 1


AND m.messageid = um.messageid
小开

Try this..

DELETE a.*, b.*
FROM table1 as a, table2 as b
WHERE a.id=[Your value here] and b.id=[Your value here]

I let id as a sample column.

Glad this helps. :)

小开

You can also use like this, to delete particular value when both the columns having 2 or many of same column name.

DELETE project , create_test  FROM project INNER JOIN create_test
WHERE project.project_name='Trail' and  create_test.project_name ='Trail' and project.uid= create_test.uid = '1';
小开

The OP is just missing the table aliases after the delete

DELETE t1, t2
FROM table1 t1 LEFT JOIN table2 t2 ON t1.id = t2.id
WHERE t1.id = some_id
小开

there's another way which is not mentioned here (I didn't fully test it's performance yet), you could set array for all tables -> rows you want to delete as below

// set your tables array
$array = ['table1', 'table2', 'table3'];




// loop through each table
for($i = 0; $i < count($array); $i++){


// get each single array
$single_array = $array[$i];


// build your query
$query = "DELETE FROM $single_array WHERE id = 'id'";


// prepare the query and get the connection
$data = con::GetCon()->prepare($query);


// execute the action
$data->execute();
}

then you could redirect the user to the home page.

header('LOCATION:' . $home_page);

hope this will help someone :)

Thanks


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