MySQL InnoDB外键问题

Question

I have the following tables and I am trying to run them in MySQL but I keep getting an errno 150. Just not sure why, but MySQL cannot seem to create the foreign key constraint. I have already looked at the rules for setting FKs for InnoDB and everything seems ok. Could someone please lend me another set of eyes and expertise?

-- Table publication_type (parent table)
CREATE TABLE publication_type (
  id int(11) UNSIGNED NOT NULL AUTO_INCREMENT,
  publication_type varchar(55)  NOT NULL,
  tstamp timestamp  NOT NULL  DEFAULT CURRENT_TIMESTAMP,
  CONSTRAINT publication_type_pk PRIMARY KEY (id)
)ENGINE=InnoDB DEFAULT CHARSET=utf8 AUTO_INCREMENT=1;

-- Table publication (child table)
CREATE TABLE publication (
  id int(11) UNSIGNED NOT NULL AUTO_INCREMENT,
  authors varchar(255)  NOT NULL,
  publication_title varchar(100)  NOT NULL,
  publication_type_id int(11) UNSIGNED NOT NULL,
  user_id int(11) UNSIGNED NOT NULL,
  CONSTRAINT publication_pk PRIMARY KEY (id),
  CONSTRAINT publication_type_fk FOREIGN KEY (publication_type_id)  REFERENCES publication_type(id) ON DELETE SET NULL ON UPDATE NO ACTION
) ENGINE=InnoDB DEFAULT CHARSET=utf8 AUTO_INCREMENT=1;

Answer 1

The types do not match:

publication_type.id is of type int UNSIGNED

publication.publication_type_id is of type int

See also the docs: http://dev.mysql.com/doc/refman/5.1/en/create-table-foreign-keys.html , specifically:

Corresponding columns in the foreign key and the referenced key must have similar data types. The size and sign of integer types must be the same . The length of string types need not be the same. For nonbinary (character) string columns, the character set and collation must be the same.

emphasis mine.