mysqlでエラー1452（23000）が発生する

Question

テーブルに日付を挿入しようとするとこのエラーが発生します。ここで

ERROR 1452 (23000): Cannot add or update a child row: a foreign key constraint fails (university . course , CONSTRAINT course_ibfk_2 FOREIGN KEY (prerequisite) REFERENCES course (course_id))

は私のテーブルです：

CREATE TABLE department (
    dept_id INT(1) UNIQUE, 
    dept_name VARCHAR(50) NOT NULL, 
    budget INT(10) NOT NULL, 
    PRIMARY KEY (dept_id))ENGINE=INNODB; 



CREATE TABLE term (
    term_id VARCHAR(50) UNIQUE, 
    term_desc VARCHAR(50) NOT NULL, 
    start_date DATE NOT NULL, 
    end_date DATE NOT NULL, 
    PRIMARY KEY (term_id))ENGINE=INNODB; 



CREATE TABLE major (
    major_id VARCHAR(3) UNIQUE, 
    major_desc VARCHAR(50) NOT NULL, 
    PRIMARY KEY (major_id))ENGINE=INNODB; 



CREATE TABLE location (
    room_id INT(2) UNIQUE, 
    building VARCHAR(50) NOT NULL, 
    room_no INT(3) NOT NULL, 
    capacity INT(2) NOT NULL, 
    room_type VARCHAR(1) NOT NULL, 
    room_description VARCHAR(50) NOT NULL, 
    PRIMARY KEY (room_id))ENGINE=INNODB; 

CREATE TABLE course 
(
    course_id VARCHAR(6), 
    title VARCHAR(30) NOT NULL UNIQUE, 
    credits INT(1) NOT NULL, 
    dept_id INT(1) NOT NULL AUTO_INCREMENT, 
    prerequisite VARCHAR(6), 
    PRIMARY KEY (course_id), 
    FOREIGN KEY (dept_id) REFERENCES department (dept_id), 
    FOREIGN KEY (prerequisite) REFERENCES course (course_id) 
) 
ENGINE=innodb; 

CREATE TABLE faculty 
(
    faculty_id INT(5), 
    name VARCHAR(30) NOT NULL, 
    room_id INT(2), 
    dept_id INT(1) NOT NULL, 
    salary DECIMAL(8,2), 
    PRIMARY KEY (faculty_id), 
    FOREIGN KEY (room_id) REFERENCES location (room_id), 
    FOREIGN KEY (dept_id) REFERENCES department (dept_id) 
) 
ENGINE=innodb; 


CREATE TABLE student 
(
    student_id INT(5), 
    last_name VARCHAR(30) NOT NULL, 
    first_name VARCHAR(30) NOT NULL, 
    street VARCHAR(60), 
    city VARCHAR(40), 
    state CHAR(2), 
    zip VARCHAR(5), 
    birth_date DATE, 
    major_id VARCHAR(3), 
    phone VARCHAR(10), 
    student_type ENUM('ugrad','grad'), 
    PRIMARY KEY (student_id), 
    FOREIGN KEY (major_id) REFERENCES major (major_id) 
) 
ENGINE=innodb; 

CREATE TABLE section 
(
    section_id INT(4), 
    course_id VARCHAR(6) NOT NULL, 
    section_number VARCHAR(2) NOT NULL, 
    term_id VARCHAR(4) NOT NULL, 
    faculty_id INT(5), 
    day VARCHAR(8), 
    max_count INT(2), 
    start_time TIME, 
    end_time TIME, 
    room_id INT(2), 
    PRIMARY KEY (section_id), 
    FOREIGN KEY (course_id) REFERENCES course (course_id), 
    FOREIGN KEY (term_id) REFERENCES term (term_id), 
    FOREIGN KEY (faculty_id) REFERENCES faculty (faculty_id), 
    FOREIGN KEY (room_id) REFERENCES location (room_id) 
); 

CREATE TABLE registration 
(
    student_id INT(5), 
    section_id INT(4), 
    midterm_grade ENUM('A','B','C','D','F','W'), 
    final_grade ENUM('A','B','C','D','F','W'), 
    PRIMARY KEY (student_id, section_id), 
    FOREIGN KEY (student_id) REFERENCES student (student_id), 
    FOREIGN KEY (section_id) REFERENCES section (section_id) 
) 
ENGINE=innodb; 

私はもちろん、テーブルに入力する私の値をしようとすると、エラーを取得セクションと、登録していると私はできる」ここに私の完全な誤りであります入力値を修正する方法を理解しているようです。私はERROR 1452（23000）を取得し、これらのテーブルへの入力値にしてみてください

INSERT INTO course (course_id, title, credits, dept_id, prerequisite) 
VALUES ('AC101', 'Accounting', '3', '3', 'EN100') 

INSERT INTO section (section_id, course_id, section, term_id, faculty_id, day, max_count, start_time, end_time, room_id) 
VALUES ('1101', 'CIS265', '01', 'WN13', '63395', 'MW', '30', '09:00', '10:30', '13') 

INSERT INTO registration (student_id, section_id, midterm_grade, final_grade) 
VALUES ('24746', '1102', 'B', 'B') 

いつでも：ここで私はもちろん、セクションおよび登録テーブルに挿入しようとしている入力値のカップルです。誰かが私が間違っている場所や値を入力する方法を理解できるように助けてくれますか？

Answer 1

ERROR 1452 (23000): Cannot add or update a child row: a foreign key constraint fails 
(`university`.`course`, CONSTRAINT `course_ibfk_2` 
FOREIGN KEY (`prerequisite`) REFERENCES `course` (`course_id`)) 

このエラーはcourseテーブルのprerequisiteカラムに投入された値がcourseテーブルの行と一致しないことを言っています。

prerequisite='EN100'の行を追加する前に、course_id='EN100'の行がテーブルに存在する必要があります。

---

これらの行を挿入します。

INSERT INTO department (dept_id, dept_name, budget) VALUES 
('1', 'Language Arts', NULL); 

INSERT INTO course (course_id, title, credits, dept_id, prerequisite) VALUES 
('EN100', 'English Composition', '3', '1', NULL) ; 

INSERT INTO department (dept_id, dept_name, budget) VALUES 
('3', 'Business', NULL); 

我々は、この行を挿入する前に：

INSERT INTO course (course_id, title, credits, dept_id, prerequisite) VALUES 
('AC101', 'Accounting', '3', '3', 'EN100') ;