mysql 建立外键出现的问题

mysql 寤哄??????跺????50??璇?

Mysql??璇?锛?error Code: 1005. Can't create table 'joblog.sc' (errno: 150)

create table sc

(

id int(10) unsigned not null auto_increment comment 'id',

Sno int(10) unsigned not null default '0' comment '瀛???,

Cno int(10) unsigned not null default '0' comment '璇剧???,

Grade int(10) unsigned default null comment '??缁?,

primary key (id),

constraint FK_sc_1 foreign key (Sno) references student(id) ,

constraint FK_sc_2 foreign key(Cno) references course(id)

)engine=InnoDB default charset=gb2312;

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??FOREIGN KEY绾?????

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