得到一个
错误代码:1822。添加外键约束失败。丢失的
引用表中约束“subject_ibfk_1”的索引
'注册'
当尝试创建subject
桌子。问题是,错误并没有出现在上一张表上student
。数据类型相同,并且定义了主键。
两者都会出现此错误enrolment
and grade
tables.
create table enrolment(
stud_id char(9) not null,
subj_code char(8) not null,
semester tinyint unsigned not null,
year smallint unsigned not null,
comment text,
primary key (stud_id, subj_code, semester, year)
);
create table grade(
stud_id char(9) not null,
subj_code char(8) not null,
semester tinyint unsigned not null,
year smallint unsigned not null,
grade tinyint unsigned,
primary key (stud_id, subj_code, semester, year)
);
create table student(
stud_id char(9) not null,
stud_name char(30),
stud_phone char(12),
stud_date_of_birth date,
stud_city char(26),
stud_address char(30),
stud_postcode char(4),
primary key (stud_id),
foreign key (stud_id)
references grade(stud_id),
foreign key (stud_id)
references enrolment(stud_id)
);
create table subject(
subj_code char(8) not null,
subj_title char(40),
primary key (subj_code),
foreign key (subj_code)
references enrolment(subj_code),
foreign key (subj_code)
references grade(subj_code)
);