Have an error where my first foreign key constraint is incorrectly formed. I'm waiting to hear back from my lecturer if she can spot the issue but thought I'd ask here
My SQL query is as follows
CREATE DATABASE rugby;
USE rugby;
CREATE TABLE address(
address_ID INT AUTO_INCREMENT NOT NULL,
address_name VARCHAR(50) NOT NULL,
PRIMARY KEY (address_ID)
) ENGINE=INNODB;
CREATE TABLE team(
team_ID INT AUTO_INCREMENT NOT NULL,
team_Name VARCHAR(25) NOT NULL,
team_Year INT NOT NULL,
PRIMARY KEY(team_ID)
) ENGINE=INNODB;
CREATE TABLE person(
person_ID INT AUTO_INCREMENT NOT NULL,
name VARCHAR(30) NOT NULL,
phone INT NOT NULL,
address_ID INT NOT NULL,
email VARCHAR(50),
photo BLOB,
PRIMARY KEY(person_ID),
FOREIGN KEY(address_ID) REFERENCES address(address_ID) ON DELETE SET NULL ON UPDATE CASCADE
) ENGINE=INNODB;
I have followed how we were taught but can't spot the issue.
Any help appreciated
In table person you have defined address_ID as NOT NULL, but
when you define the FOREIGN KEY you set:
ON DELETE SET NULL
which contradicts the NOT NULL definition.
Related
Somehow I can't create a join table for two entities I already have.
Here is what I run on MySQL just fine, the last one is the one I'm struggling with.
create table instructor_detail_table(
instructor_detail_id int not null primary key auto_increment,
instructor_class varchar(40) not null
);
create table instructor_table(
instructor_id int not null primary key auto_increment,
instructor_name varchar(40) not null,
instructor_detail_id int not null,
foreign key (instructor_detail_id) references instructor_detail_table (instructor_detail_id)
);
create table course_table(
course_id int not null primary key auto_increment,
course_class varchar(40) not null,
instructor_id int not null,
foreign key (instructor_id) references instructor_table (instructor_id)
);
create table student_table(
student_id int not null primary key auto_increment,
student_name varchar(40) not null,
student_age int not null
);
create table student_course_table(
student_id int not null,
course_id int not null,
foreign key (student_id) references student_table (student_id),
foreign key (course_id) references course_table (course_id),
primary key (student_id, course_id)
);
When I try to create the student_course_table MySQL complaints it can't open the referenced table student_table
Thanks in advance
You can have this problem if the storage engine is not the good one.
For example 'MyISAM' instead of 'InnoDB' for the table 'student_table'.
Because MyISAM doesn't support foreign key.
so pretty new to SQL I created 2 tables which I wanted to be related to one another but I'm getting an error "#1215 - Cannot add foreign key constraint" can someone point me to the right direction of this problem?
CREATE TABLE movie(
id INT(1) NOT NULL AUTO_INCREMENT,
nearname VARCHAR(25) NOT NULL,
release_date DATE NOT NULL,
lang VARCHAR(10) NOT NULL,
PRIMARY KEY(id),
CONSTRAINT same_movie FOREIGN KEY(id) REFERENCES movie_cast(movie_id)
);
CREATE TABLE movie_cast(
movie_id INT(1) NOT NULL AUTO_INCREMENT,
director_name VARCHAR(20) NOT NULL,
actor_name VARCHAR(20) NOT NULL,
actress_name VARCHAR(20) NOT NULL,
PRIMARY KEY(movie_id),
CONSTRAINT same_movie FOREIGN KEY(movie_id) REFERENCES movie(id)
);
You need to refer to the same column name as the primary key. In this case, it is called id:
CONSTRAINT same_movie FOREIGN KEY(movie_id) REFERENCES movie_cast(id)
Of course, your DDL doesn't define movie_cast. So, I am guessing the second table should be something like:
CREATE TABLE movie_cast (
id INT NOT NULL AUTO_INCREMENT,
movie_id int not null,
cast_name varchar(255)
PRIMARY KEY(id),
CONSTRAINT fk_movie_cast_movie FOREIGN KEY(movie_id) REFERENCES movie(movie_id)
);
this is my code:
CREATE DATABASE exams;
SHOW DATABASES;
CREATE TABLE IF NOT EXISTS students(
student_id INT UNSIGNED NOT NULL AUTO_INCREMENT,
first_name VARCHAR(20) NOT NULL,
middle_name VARCHAR(40),
last_name VARCHAR(40)NOT NULL,
email VARCHAR(60) NOT NULL,
password CHAR(40) NOT NULL,
reg_date DATETIME NOT NULL,
PRIMARY KEY (student_id),
UNIQUE(email));
SHOW table status
INSERT INTO exams_3121(student_id, first_name, middle_name, last_name, email, password, reg_date)
CREATE TABLE entries
(
entrie_id int NOT NULL,
student_id int NOT NULL,
subject_id int,
PRIMARY KEY (entrie_id),
FOREIGN KEY (student_id) REFERENCES student(student_id),
FOREIGN KEY (subject_id)REFERENCES subject(subject_id)
)
CREATE DATABASE subjects;
CREATE TABLE IF NOT EXISTS subjects(
subject_id INT UNSIGNED NOT NULL AUTO_INCREMENT,
subject_name VARCHAR(20) NOT NULL,
level_entery VARCHAR(40)NOT NULL,
exam_board VARCHAR(60) NOT NULL,
PRIMARY KEY (subject_id));
CREATE TABLE entries
(
entrie_id int NOT NULL,
entrie_id int NOT NULL,
subject_id int,
PRIMARY KEY (entrie_id),
FOREIGN KEY (student_id) REFERENCES student(student_id),
FOREIGN KEY (subject_id)REFERENCES subject(subject_id)
)
When I use this code it says cannot add foreign key constraint
and I don't know what to do. Please and thanks in advance.
There are two problems.
First, you got the names of the table you're referencing wrong. The name of the tables are students and subjects, but you wrote student and subject.
Second, the entries table has two entrie_id columns. One of them should be student_id.
CREATE TABLE entries
(
entrie_id int NOT NULL,
student_id int NOT NULL,
subject_id int,
PRIMARY KEY (entrie_id),
FOREIGN KEY (student_id) REFERENCES students(student_id),
FOREIGN KEY (subject_id) REFERENCES subjects(subject_id)
)
Also, if you're creating multiple databases and putting your tables in them, you'll need to refer to tables with their database prefixes if they're different from the one you selected as default with the USE command. As you've written it, you're not actually using the databases you created with CREATE DATABASE.
I have researched thoroughly before asking this question including on this site.
I have a students table:
CREATE TABLE IF NOT EXISTS students(
student_id INT UNSIGNED NOT NULL AUTO_INCREMENT,
first_name VARCHAR(20) NOT NULL,
middle_name VARCHAR(20),
last_name VARCHAR(40) NOT NULL,
email VARCHAR(60) NOT NULL,
password CHAR(40) NOT NULL,
reg_date DATETIME NOT NULL,
PRIMARY KEY (student_id),
UNIQUE (email));
I also have a subjects table:
CREATE TABLE IF NOT EXISTS subjects(
subject_id INT UNSIGNED NOT NULL AUTO_INCREMENT,
subject_name VARCHAR(40) NOT NULL,
level_of_entry VARCHAR(20) NOT NULL,
exam_board VARCHAR(20) NOT NULL,
PRIMARY KEY (subject_id));
I am now creating a table to link the above tables:
CREATE TABLE IF NOT EXISTS entries(
exam_date DATETIME NOT NULL,
FOREIGN KEY (student_id) REFERENCES students (student_id),
FOREIGN KEY (subject_id) REFERENCES subjects (subject_id)
);
My problem is that when I try to declare the foreign keys in the third table called entries, I get an error stating that the subject_id foreign key is not in the table referenced.
ERROR 1072 (42000) : Key column 'student_id' doesn't exist in table, even though it is clearly contained inside the the students table and the same applies to 'subject_id' and the subject table.
I am certain that my syntax for declaring the foreign keys is correct so I am unsure how to fix the problem.
All help is appreciated. Thank you.
You forgot to create these two columns before applying your foreign key constraints :
CREATE TABLE IF NOT EXISTS entries(
exam_id INT UNSIGNED NOT NULL AUTO_INCREMENT,
student_id INT UNSIGNED NOT NULL,
subject_id INT UNSIGNED NOT NULL,
exam_date DATETIME NOT NULL,
PRIMARY KEY (exam_id),
FOREIGN KEY (student_id) REFERENCES students (student_id),
FOREIGN KEY (subject_id) REFERENCES subjects (subject_id)
);
EDIT :
I advise you to add in every table a unique ID column (here : exam_id).
MySQL:
CREATE SCHEMA IF NOT EXISTS otes_db;
USE otes_db;
CREATE TABLE IF NOT EXISTS school(
school_code CHAR(3),
school_desc VARCHAR(255) NOT NULL,
school_head INT UNSIGNED NOT NULL,
PRIMARY KEY(school_code),
FOREIGN KEY(school_head) REFERENCES user(user_id)
ON DELETE CASCADE
ON UPDATE CASCADE
)ENGINE=INNODB;
CREATE TABLE IF NOT EXISTS user(
user_id INT UNSIGNED,
user_lname VARCHAR(255) NOT NULL,
user_fname VARCHAR(255) NOT NULL,
user_mname VARCHAR(255),
user_email VARCHAR(255) UNIQUE NOT NULL,
user_password VARCHAR(255) NOT NULL,
user_type ENUM('CEO', 'VP', 'HEAD', 'CHAIR', 'STUD') NOT NULL,
user_isActivated ENUM('Y', 'N') DEFAULT 'N',
PRIMARY KEY(user_id)
);
Based on this thread, I have checked for the following:
InnoDB Engine is set in school table
The referenced key is a primary key (user_id)
The data types are the same (INT UNSIGNED)
However, I'm still getting the error with the school_head and user_id. Anything I missed?
You need to create the user table first