MySQL 的级联删除

create table students(
	id bigint not null primary key auto_increment,
	sid varchar(20) not null,
	name varchar(20) not null,
	age tinyint unsigned not null,
	gender varchar(10) not null,
	cid bigint not null,
	index(cid),
	constraint foreign key(cid) references school_class(id) on delete cascade
) engine=Innodb, charset=utf8;

create table students( id bigint not null primary key auto_increment, sid varchar(20) not null, name varchar(20) not null, age tinyint unsigned not null, gender varchar(10) not null, cid bigint not null, index(cid), constraint foreign key(cid) references school_class(id) on delete cascade ) engine=Innodb, charset=utf8;