ERROR 1451（2300）：不能删除或更新父行，外键约束失败

Question

DROP TABLE if exists employee; 
CREATE TABLE employee (
    fname varchar(15) not null, 
    minit varchar(1), 
    lname varchar(15) not null, 
    ssn  char(9), 
    bdate date, 
    address varchar(50), 
    sex  char, 
    salary decimal(10,2), 
    superssn char(9), 
    dno  int(4), 
    primary key (ssn), 
    foreign key (superssn) references employee(ssn) 
-- foreign key (dno) references department(dint) 
); 

DROP TABLE if exists department; 
CREATE TABLE department (
    dname  varchar(25) not null, 
    dint  int(4), 
    mgrssn  char(9) not null, 
    mgrstartdate date, 
    primary key (dint), 
    unique (dname), 
    foreign key (mgrssn) references employee(ssn) 
); 

ALTER TABLE employee ADD (
    foreign key (dno) references department(dint) 
); 

DROP TABLE if exists dept_locations; 
CREATE TABLE dept_locations (
    dint int(4), 
    dlocation varchar(15), 
    primary key (dint,dlocation), 
    foreign key (dint) references department(dint) 
); 

DROP TABLE if exists project; 
CREATE TABLE project (
    pname  varchar(25) not null, 
    pint int(4), 
    plocation varchar(15), 
    dnum  int(4) not null, 
    primary key (pint), 
    unique (pname), 
    foreign key (dnum) references department(dint) 
); 

DROP TABLE if exists works_on; 
CREATE TABLE works_on (
    essn char(9), 
    pno int(4), 
    hours decimal(4,1), 
    primary key (essn,pno), 
    foreign key (essn) references employee(ssn), 
    foreign key (pno) references project(pint) 
); 

DROP TABLE if exists dependent; 
CREATE TABLE dependent (
    essn   char(9), 
    dependent_name varchar(15), 
    sex   char, 
    bdate   date, 
    relationship varchar(8), 
    primary key (essn,dependent_name), 
    foreign key (essn) references employee(ssn) 
); 

Answer 1

的错误是在这条线ALTER TABLE employee ADD (...

请编辑并使它看起来像：

ALTER TABLE employee ADD 
    foreign key (dno) references department(dint); 

有一些不必要的括号。