这外键老是报错150，我这是哪错了？
CREATE TABLE `peovinces` (
`id` smallint(5) unsigned NOT NULL AUTO_INCREMENT,
`pname` varchar(20) NOT NULL,
PRIMARY KEY (`id`)
) ENGINE=InnoDB DEFAULT CHARSET=utf8;
CREATE TABLE users(
id SMALLINT UNSIGNED PRIMARY KEY AUTO_INCREMENT,
username VARCHAR(10) NOT NULL,
pid smallint UNSIGNED,
FOREIGN KEY (pid) REFERENCES provinces (id)
);
