1. Referential Integrity MySQL
CREATE TABLE exmp1( id INT NOT NULL, val TEXT, UNIQUE (id) ) TYPE=InnoDB;
CREATE TABLE exmp2( id INT, blah TEXT, INDEX(id), CONSTRAINT id_fkey FOREIGN KEY (id) REFERENCES exmp1(id) ON UPDATE CASCADE ) TYPE=InnoDB;

2. Examples:Zoo animals
CREATE TABLE species (id TINYINT NOT NULL AUTO_INCREMENT, name VARCHAR(50) NOT NULL, PRIMARY KEY(id)) TYPE=INNODB;
INSERT INTO species VALUES (1, 'orangutan'), (2, 'elephant'), (3, 'hippopotamus'), (4, 'yak');
CREATE TABLE zoo (id INT(4) NOT NULL, name VARCHAR(50) NOT NULL, FK_species TINYINT(4) NOT NULL, INDEX (FK_species), constraint FOREIGN KEY (FK_species) REFERENCES species (id) on update cascade, PRIMARY KEY(id)) TYPE=INNODB;
INSERT INTO zoo VALUES (1, 'Harry', 5); //error:violate R.I.
INSERT INTO zoo VALUES (1, 'Harry', 2);//OK
Update species set id=5 where name=‘elephant’;//change zoo too