Question

I’m trying to use SQL to delete multiple rows from multiple tables that are joined together.

Table A is joined to Table B Table B is joined to Table C

I want to delete all rows in table B & C that correspond to a row in Table A

CREATE TABLE `boards` (   `boardid` int(2) NOT NULL AUTO_INCREMENT,   `boardname` varchar(255) NOT NULL DEFAULT '',   PRIMARY KEY  (`boardid`) );  -- --------------------------------------------------------  --  -- Table structure for table `messages` --   CREATE TABLE `messages` (   `messageid` int(6) NOT NULL AUTO_INCREMENT,   `boardid` int(2) NOT NULL DEFAULT '0',   `topicid` int(4) NOT NULL DEFAULT '0',   `message` text NOT NULL,   `author` varchar(255) NOT NULL DEFAULT '',   `date` datetime DEFAULT NULL,   PRIMARY KEY  (`messageid`) );  -- --------------------------------------------------------  --  -- Table structure for table `topics` --   CREATE TABLE `topics` (   `topicid` int(4) NOT NULL AUTO_INCREMENT,   `boardid` int(2) NOT NULL DEFAULT '0',   `topicname` varchar(255) NOT NULL DEFAULT '',   `author` varchar(255) NOT NULL DEFAULT '',   PRIMARY KEY  (`topicid`) ); 

Answer 1

Well, if you had used InnoDB tables, you could set up a cascading delete with foreign keys that would do it all automatically. But if you have some reason for using MyISAM, You just use a multiple-table DELETE:

DELETE FROM boards, topics, messages USING boards INNER JOIN topics INNER JOIN messages WHERE boards.boardid = $boardid     AND topics.boardid = boards.boardid     AND messages.boardid = boards.boardid;