Question

I’m having problems to truncate a table on the MySQL Server 5.5.

The table I’m trying to truncate has a column that serves as a foreign key in another table.

The CREATE TABLE of both tables involved is as it follows:

CREATE TABLE `tbluser` (
  `id` int(11) NOT NULL AUTO_INCREMENT,
  `email` varchar(255) NOT NULL,
  `password` varchar(255) NOT NULL,
  `name` varchar(255) NOT NULL,
  `creationDate` datetime NOT NULL,
  `creationUserId` int(11) NOT NULL,
  `updateDate` datetime NOT NULL,
  `updateUserId` int(11) NOT NULL,
  `lastAccess` datetime NOT NULL,
  `enabled` tinyint(1) NOT NULL,
  PRIMARY KEY (`id`),
  UNIQUE KEY `id_UNIQUE` (`id`),
  UNIQUE KEY `email_UNIQUE` (`email`),
  KEY `FK_tbluser_creationUserId` (`creationUserId`),
  KEY `FK_tbluser_updateUserId` (`updateUserId`),
  CONSTRAINT `FK_tbluser_updateUserId` FOREIGN KEY (`updateUserId`) REFERENCES `tbluser` (`id`) ON DELETE CASCADE ON UPDATE CASCADE,
  CONSTRAINT `FK_tbluser_creationUserId` FOREIGN KEY (`creationUserId`) REFERENCES `tbluser` (`id`) ON DELETE CASCADE ON UPDATE CASCADE
) ENGINE=InnoDB AUTO_INCREMENT=5 DEFAULT CHARSET=latin1;

CREATE TABLE `tblpost` (
  `id` int(11) NOT NULL AUTO_INCREMENT,
  `title` varchar(255) NOT NULL,
  `content` mediumtext NOT NULL,
  `creationDate` datetime NOT NULL DEFAULT '1901-01-01 00:00:00',
  `creationUserId` int(11) NOT NULL,
  `updateDate` datetime NOT NULL DEFAULT '1901-01-01 00:00:00',
  `updateUserId` int(11) NOT NULL,
  PRIMARY KEY (`id`),
  KEY `FK_tblpost_creationUserId` (`creationUserId`),
  KEY `FK_tblpost_updateUserId` (`updateUserId`),
  CONSTRAINT `FK_tblpost_updateUserId` FOREIGN KEY (`updateUserId`) REFERENCES `tbluser` (`id`) ON DELETE CASCADE ON UPDATE CASCADE,
  CONSTRAINT `FK_tblpost_creationUserId` FOREIGN KEY (`creationUserId`) REFERENCES `tbluser` (`id`) ON DELETE CASCADE ON UPDATE CASCADE
) ENGINE=InnoDB DEFAULT CHARSET=latin1;

Please note that all the constraints are both set to DELETE and UPDATE ON CASCADE.

When I try to TRUNCATE the table:

TRUNCATE TABLE `<databasename>`.`tbluser`;

I receive the following error message:

Cannot truncate a table referenced in a foreign key constraint
(`<databasename>`.`tblpost`, 
CONSTRAINT `FK_tblpost_updateUserId` 
FOREIGN KEY (`updateUserId`) 
REFERENCES `<databasename>`.`tbluser` (`id`))

In addition to this information, there is the fact that when the action above is attempted on a MySQL Server 5.1, it works!

Does anyone have an idea of why this is happening?

Answer 1

Check here . That makes sense that TRUNCATE TABLE raises an error in such cases; the bad thing that it’s not documented.