＃1215 - 不能添加外键约束

Question

无法创建表由于

1215 - 不能添加外键约束

有什么问题吗？ 是语法错误还是逻辑错误？ 当我省略外键约束线，它工作正常。

create table classroom 
    (building  varchar(15), 
    room_number  varchar(7), 
    capacity  numeric(4,0), 
    primary key (building, room_number) 
    ); 
create table department 
    (dept_name  varchar(20), 
    building  varchar(15), 
    budget    numeric(12,2) check (budget > 0), 
    primary key (dept_name) 
    ); 

create table course 
    (course_id  varchar(8), 
    title   varchar(50), 
    dept_name  varchar(20), 
    credits  numeric(2,0) check (credits > 0), 
    primary key (course_id), 
    foreign key (dept_name) references department 
     on delete set null 
    ); 

create table instructor 
    (ID   varchar(5), 
    name   varchar(20) not null, 
    dept_name  varchar(20), 
    salary   numeric(8,2) check (salary > 29000), 
    primary key (ID), 
    foreign key (dept_name) references department 
     on delete set null 
    ); 

create table section 
    (course_id  varchar(8), 
     sec_id   varchar(8), 
    semester  varchar(6) 
     check (semester in ('Fall', 'Winter', 'Spring', 'Summer')), 
    year   numeric(4,0) check (year > 1701 and year < 2100), 
    building  varchar(15), 
    room_number  varchar(7), 
    time_slot_id  varchar(4), 
    primary key (course_id, sec_id, semester, year), 
    foreign key (course_id) references course 
     on delete cascade, 
    foreign key (building, room_number) references classroom 
     on delete set null 
    ); 

create table teaches 
    (ID   varchar(5), 
    course_id  varchar(8), 
    sec_id   varchar(8), 
    semester  varchar(6), 
    year   numeric(4,0), 
    primary key (ID, course_id, sec_id, semester, year), 
    foreign key (course_id,sec_id, semester, year) references section 
     on delete cascade, 
    foreign key (ID) references instructor 
     on delete cascade 
    ); 

create table student 
    (ID   varchar(5), 
    name   varchar(20) not null, 
    dept_name  varchar(20), 
    tot_cred  numeric(3,0) check (tot_cred >= 0), 
    primary key (ID), 
    foreign key (dept_name) references department 
     on delete set null 
    ); 

create table takes 
    (ID   varchar(5), 
    course_id  varchar(8), 
    sec_id   varchar(8), 
    semester  varchar(6), 
    year   numeric(4,0), 
    grade    varchar(2), 
    primary key (ID, course_id, sec_id, semester, year), 
    foreign key (course_id,sec_id, semester, year) references section 
     on delete cascade, 
    foreign key (ID) references student 
     on delete cascade 
    ); 

create table advisor 
    (s_ID   varchar(5), 
    i_ID   varchar(5), 
    primary key (s_ID), 
    foreign key (i_ID) references instructor (ID) 
     on delete set null, 
    foreign key (s_ID) references student (ID) 
     on delete cascade 
    ); 

create table time_slot 
    (time_slot_id  varchar(4), 
    day   varchar(1), 
    start_hr  numeric(2) check (start_hr >= 0 and start_hr < 24), 
    start_min  numeric(2) check (start_min >= 0 and start_min < 60), 
    end_hr   numeric(2) check (end_hr >= 0 and end_hr < 24), 
    end_min  numeric(2) check (end_min >= 0 and end_min < 60), 
    primary key (time_slot_id, day, start_hr, start_min) 
    ); 

create table prereq 
    (course_id  varchar(8), 
    prereq_id  varchar(8), 
    primary key (course_id, prereq_id), 
    foreign key (course_id) references course 
     on delete cascade, 
    foreign key (prereq_id) references course 
    ); 

Answer 1

就像我所做的那样，您必须在外键引用的表名的括号前面添加dept_name。 例如：

create table course 
    (course_id  varchar(8), 
    title   varchar(50), 
    dept_name  varchar(20), 
    credits  numeric(2,0) check (credits > 0), 
    primary key (course_id), 
    foreign key (dept_name) references department(dept_name) 
     on delete set null 
    );