MySQL workbench error

[Nodral]

Hi I'm trying to set a foreign key to link tables within MySQL workbench and cannot work out why I'm getting the folowing error.

SQL Error 1005: Can't create table 'feedback.#sql-174_8' (errno: 150)

The SQL I'm trying to run is

ALTER TABLE `feedback`.`question_answers`

ADD CONSTRAINT `relation`

FOREIGN KEY (`relation` )

REFERENCES `feedback`.`user` (`relation` )

ON DELETE SET NULL

ON UPDATE CASCADE

, ADD INDEX `relation` (`relation` ASC) ;

The DB is called 'feedback' and I have tables called 'user' and 'question_answers' Both of the relation fields are set as (VARCHAR45) and I cannot get this link to function.

Any ideas?

[r937]

could you do a SHOW CREATE TABLE for both tables please

[Nodral]

CREATE TABLE `user` (
`iduser` int(11) NOT NULL AUTO_INCREMENT,
`firstname` varchar(255) NOT NULL,
`surname` varchar(255) NOT NULL,
`relation` varchar(45) NOT NULL,
PRIMARY KEY (`iduser`)
) ENGINE=InnoDB DEFAULT CHARSET=utf8

'CREATE TABLE `question_answers` (
`idquestion_answers` int(11) NOT NULL AUTO_INCREMENT,
`idquestion` int(11) NOT NULL,
`relation` varchar(45) NOT NULL,
`answer` varchar(255) NOT NULL,
PRIMARY KEY (`idquestion_answers`),
KEY `idquestion` (`idquestion`),
CONSTRAINT `idquestion` FOREIGN KEY (`idquestion`) REFERENCES `question_text` (`idquestion`) ON DELETE CASCADE ON UPDATE CASCADE
) ENGINE=InnoDB DEFAULT CHARSET=utf8'

[r937]

ALTER TABLE user ADD UNIQUE (relation)

this allows relation to be the target of the REFERENCES in question_answers