Cannot add foreign key constraint？

Question

mysql> CREATE TABLE province(    -> id TINYINT UNSIGNED PRIMARY KEY AUTO_INCREMENT,    -> pname VARCHAR(20) NOT NULL    -> );Query OK, 0 rows affected (0.04 sec)mysql> CREATE TABLE users(    -> id TINYINT UNSIGNED PRIMARY KEY AUTO_INCREMENT,    -> username VARCHAR(20) NOT NULL,    -> pid TINYINT,    -> FOREIGN KEY (pid) REFERENCES province (id)    -> );ERROR 1215 (HY000): Cannot add foreign key constraint

Answer 1

刚发现了问题。id和pid没有同意符号位。