====== InnoDB Foreign Keys =====

==== Features ====

  * Forces database consistency
  * No need to rely on application for referential integrity

==== Usage ====

  * Primary use is for parent-child table relationships
  * Parent-child relationships can exist within the same table
  * Column types for both indexes must be exactly the same
  * Character set must also be the same for non-binary columns
  * InnoDB rejects any creation of records where the constraints do not match
  * You can use ALTER TABLE to retroactively apply a foreign key match, but the indexes must be valid
  * Use ''SHOW CREATE TABLE'' to display foreign key indexes

==== Notes ====

  * MyISAM tables will accept the syntax, but not actually do anything

==== Examples ====

Parent-child relationship in two tables:

<code>
CREATE TABLE parent (id INT NOT NULL,
                     PRIMARY KEY (id)
) ENGINE=INNODB;
CREATE TABLE child (id INT, parent_id INT,
                    INDEX par_ind (parent_id),
                    FOREIGN KEY (parent_id) REFERENCES parent(id)
                      ON DELETE CASCADE
) ENGINE=INNODB;
</code>