当我尝试在MySQL中创建一个表时，它给出了错误代码1215：“无法添加外键约束”

Question

我正在尝试创建一个数据库，但是当我运行此代码时，它会给我以下错误

code 1215: “Cannot add foreign key constraint”

drop database if exists kat_db;
create database if not exists kat_db;
use kat_db;
create table if not exists Patients(
PatientID int not null PRIMARY KEY,
PatientName varchar(50),
TypeOfAnimal varchar(50),
DateOfLastApt date,
PatientAge int,
Microchipped boolean,
OwnerID int not null,
DoctorID int not null,
foreign key (OwnerID) references Owners(OwnerID),
foreign key (DoctorID) references Doctors(DoctorID)
);

create table if not exists Owners(
OwnerID int not null PRIMARY KEY,
OwnerFirstName varchar(50),
OwnerLastName varchar(50),
PatientID int,
OwnerPhone int,
OwnerZip int,
PrefferedPaymentMethod varchar(50),
foreign key (PatientID) references Patients(PatientID)
);

create table if not exists Doctors(
DoctorID int not null PRIMARY KEY,
DoctorFirstName varchar(50),
DoctorLastName varchar(50),
PatientID int,
DoctorPhone int,
DoctorZip int,
AnimalSpecialty varchar(50),
foreign key (PatientID) references Patients(PatientID)
);

insert into Patients
(PatientID, TypeOfAnimal, PatientAge, PatientName, DateOfLastApt, Microchipped, DoctorID, OwnerID)
values 
(01, 'dog', 6, 'Dima', '2017-02-05', 1, 101, 1001),
(02, 'dog', 3, 'Misha', '2017-02-05', 1, 102, 1002),
(03, 'cat', 2, 'Pistol', '2017-06-09', 0, 103, 1003),
(04, 'cat', 1, 'Nessie', '2017-09-04', 0, 104, 1004),
(05, 'cat', 2, 'Charlie', '2016-06-04', 1, 105, 1005),
(06, 'cat', 12, 'Francis', '2015-05-07', 1, 106, 1006),
(07, 'rabbit', 5, 'Bunny', '2015-05-06', 0, 107, 1007),
(08, 'turtle', 6, 'Aqua', '2017-06-08', 0, 108, 1008),
(09, 'dog', 16, 'Sammie', '2012-09-07', 1, 109, 1009),
(10, 'dog', 14, 'Dog', '2016-04-06', 0, 110, 1010)
;

insert into Owners
(OwnerID, OwnerFirstName, OwnerLastName, OwnerPhone, OwnerZip, PrefferedPaymentMethod, PatientID)
values 
(101, 'Kat', 6, 'Dima', '2017-02-05', 1, 101, 1001),
(102, 'Hunter', 3, 'Misha', '2017-02-05', 1, 102, 1002),
(103, 'Vicky', 2, 'Pistol', '2017-06-09', 0, 103, 1003),
(104, 'Vasnessa', 1, 'Nessie', '2017-09-04', 0, 104, 1004),
(105, 'Weston', 2, 'Charlie', '2016-06-04', 1, 105, 1005),
(106, 'Jonas', 12, 'Francis', '2015-05-07', 1, 106, 1006),
(107, 'Devin', 5, 'Bunny', '2015-05-06', 0, 107, 1007),
(108, 'Grego', 6, 'Aqua', '2017-06-08', 0, 108, 1008),
(109, 'Jackson', 16, 'Sammie', '2012-09-07', 1, 109, 1009),
(110, 'dog', 14, 'Dog', '2016-04-06', 0, 110, 1010)
;

insert into Patients
(PatientID, TypeOfAnimal, PatientAge, PatientName, DateOfLastApt, Microchipped, DoctorID, OwnerID)
values 
(01, 'dog', 6, 'Dima', '2017-02-05', 1, 101, 1001),
(02, 'dog', 3, 'Misha', '2017-02-05', 1, 102, 1002),
(03, 'cat', 2, 'Pistol', '2017-06-09', 0, 103, 1003),
(04, 'cat', 1, 'Nessie', '2017-09-04', 0, 104, 1004),
(05, 'cat', 2, 'Charlie', '2016-06-04', 1, 105, 1005),
(06, 'cat', 12, 'Francis', '2015-05-07', 1, 106, 1006),
(07, 'rabbit', 5, 'Bunny', '2015-05-06', 0, 107, 1007),
(08, 'turtle', 6, 'Aqua', '2017-06-08', 0, 108, 1008),
(09, 'dog', 16, 'Sammie', '2012-09-07', 1, 109, 1009),
(10, 'dog', 14, 'Dog', '2016-04-06', 0, 110, 1010)
;

我尝试以不同的顺序创建表。我还创建了一个不同的数据库，它工作，实际上，我用它来创建顶部的数据库。

drop database if exists kat3_db;
create database if not exists kat3_db;
use kat3_db;
create table if not exists Book(
BookNumber int not null,
BookName varchar(50),
BookPrice decimal(5,2),
CoverType varchar(15) default 'hardcover',
PublicationDate date,
primary key (BookNumber)
);

create table if not exists Course(
CourseNo int not null,
CourseName varchar(20),
Semester varchar(10),
BookNumber int not null,
primary key (CourseNo),
foreign key (BookNumber) references Book(BookNumber)
);

insert into Book
(BookNumber, BookName, BookPrice, CoverType, PublicationDate)
values 
(1, 'Math', 023.64, 'paperback', '1999-02-05'),
(3, 'English', 999.36, 'e-book', '2013-06-04'),
(5, 'Calc', 056.69, 'paperback', '1964-05-05'),
(6, 'C++', 053.98, 'paperback', '2016-03-04'),
(7, 'Programming', 113.02, 'paperback', '2001-10-11'),
(9, 'Art', 250.99, 'paperback', '1996-11-11'),
(10, 'Networking', 036.64, 'e-book', '2014-05-06'),
(12, 'Drawing', 111.36, 'paperback', '2013-06-04'),
(13, 'Robotics', 012.03, 'e-book', '2016-06-05'),
(14, 'Computer', 25.03, 'e-book', '2001-06-04')
;

insert into Book
(BookNumber, BookName, BookPrice, PublicationDate)
values
(2, 'Reading', 364.20, '2016-06-05'),
(4, 'Database', 036.64, '2017-06-05'),
(8, 'Wellness', 050.00, '1999-10-10'),
(11, 'Linux', 55.36, '2013-06-08'),
(15, 'FYE', 03.01, '1991-02-05')
;

insert into Course
(CourseNo, CourseName, Semester, BookNumber)
values
(111, 'IntroToMath', 'Spring', 1),
(222, 'IntroToReading', 'Fall', 2),
(333, 'IntroToEnglish', 'Spring', 3),
(444, 'IntroToDatabase', 'Fall', 4),
(555, 'IntroToCalc', 'Spring', 5),
(666, 'IntroToC++', 'Spring', 6),
(777, 'IntroToProgramming', 'Fall', 7),
(888, 'IntroToWellness','Spring', 8),
(999, 'IntroToArt', 'Fall', 9),
(010, 'IntroToNetworking', 'Spring', 10),
(011, 'IntroToLinux', 'Fall', 11),
(012, 'IntroToDrawing', 'Spring', 12),
(013, 'IntroToRobotics', 'Fall', 13),
(014, 'IntroToComputer', 'Spring', 14),
(015, 'IntroToFYE', 'Summer', 15)
;

我不知道我做了什么不同的事情。任何建议将不胜感激。如果有人可以在顶部运行第一个代码并告诉我它是否适用于他们，那也将是很大的帮助。谢谢！

Answer 1

在创建患者表时，所有者和医生表信息不可用。所以它不允许你。

所以先创建表。然后使用alter table添加FK。

Answer 2

您正在以错误的顺序添加表格。

在创建它们依赖的表/字段之前，您可以使用外键约束创建Patients表。