無法與國外關鍵是一級

Question

添加外鍵約束我收到

Error Code: 1215. Cannot add foreign key constraint 0.172 sec 

我不知道我做錯了。我確信外鍵是主鍵。 我的SQL：

CREATE TABLE Student (
StudentID INT(6) NOT NULL, 
StudName VARCHAR(15) NOT NULL, 
StudEmail VARCHAR(15) NOT NULL, 
StudeHomeNum INT(10) NOT NULL, 
StudCellPhoneNum INT(10) NOT NULL, 
CourseCode INT(6) NOT NULL, 
ProgramCode INT(6) NOT NULL, 
PRIMARY KEY (StudentID), 
FOREIGN KEY (CourseCode) 
    REFERENCES Course (CourseCode) 
); 

CREATE TABLE Course (
CourseCode INT(6) PRIMARY KEY NOT NULL, 
CourseName VARCHAR(15) NOT NULL, 
Prequisites VARCHAR(15) NOT NULL 
); 

Answer 1

由於CourseCode代碼列Student表引用Course表，您必須首先創建Course表。更改您的sql代碼如下

CREATE TABLE Course (
CourseCode INT(6) PRIMARY KEY NOT NULL, 
CourseName VARCHAR(15) NOT NULL, 
Prequisites VARCHAR(15) NOT NULL 
); 

CREATE TABLE Student (
StudentID INT(6) NOT NULL, 
StudName VARCHAR(15) NOT NULL, 
StudEmail VARCHAR(15) NOT NULL, 
StudeHomeNum INT(10) NOT NULL, 
StudCellPhoneNum INT(10) NOT NULL, 
CourseCode INT(6) NOT NULL, 
ProgramCode INT(6) NOT NULL, 
PRIMARY KEY (StudentID), 
FOREIGN KEY (CourseCode) 
    REFERENCES Course (CourseCode) 
);