Question

I am using the following SQL to create a table named app_info:

CREATE TABLE IF NOT EXISTS `app_info` (
`_id` int(11) NOT NULL AUTO_INCREMENT,
`app_name` varchar(50) DEFAULT NULL,
`app_owner` varchar(50) DEFAULT NULL,
`last_update` timestamp NULL DEFAULT CURRENT_TIMESTAMP ON UPDATE CURRENT_TIMESTAMP,
PRIMARY KEY (`_id`)
) ENGINE=MyISAM  DEFAULT CHARSET=latin1 AUTO_INCREMENT=6 ;

I am using the following SQL to create a table named tab_info:

CREATE  TABLE `myDB`.`tab_info` (
`_id` INT NOT NULL AUTO_INCREMENT ,
`app_id` INT NOT NULL ,
`tab_title` VARCHAR(15) NOT NULL ,
PRIMARY KEY (`_id`) ,
UNIQUE INDEX `app_id_UNIQUE` (`app_id` ASC) ,
INDEX `app_tab_key` (`app_id` ASC) ,
CONSTRAINT `app_tab_key`
  FOREIGN KEY (`app_id` )
  REFERENCES `myDB`.`app_info` (`_id` )
  ON DELETE CASCADE
  ON UPDATE CASCADE); 

But when I delete data from primary key table, the orphaned rows in the foreign key table are not being deleted automatically. Does anyone know what the problem could be?

Answer 1

The MyISAM storage engine doesn’t support foreign key constraints. The constraint is parsed but silently ignored.

To fix your problem use the InnoDB engine instead (for both tables).

CREATE TABLE ( ... ) ENGINE = InnoDB ... ;

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Instead of dropping your tables and recreating them you can also change the storage engine:

ALTER TABLE myDB.app_info ENGINE = InnoDB;
ALTER TABLE myDB.tab_info ENGINE = InnoDB;

After changing the engine you will need to add the foreign key constraint again.