Error Code: 1215. Cannot add foreign key constraint (foreign keys)
database, mysql
Solution
The most likely issue is this line:
FOREIGN KEY (classLeader) REFERENCES student(studentID),
The datatype of classLeader is VARCHAR(255). That has to match the datatype of the referenced column... `student.studentID`. And of course, the `student` table has to exist, and the `studentID` column has to exist, and the `studentID` column should be the PRIMARY KEY of the student table (although I believe MySQL allows this to be a UNIQUE KEY, rather than a PRIMARY KEY, or even just have an index on it.)
In any case, what's missing here is the output from `SHOW CREATE TABLE student;`
There's a datatype mismatch.
The `classLeader VARCHAR(255)` column cannot be a foreign key reference to `studentID INT`.
The datatypes of the two columns has to match.
Problem
``` CREATE DATABASE my_db; CREATE TABLE class ( classID int NOT NULL AUTO_INCREMENT, nameClass varchar(255), classLeader varchar(255), FOREIGN KEY (classLeader) REFERENCES student(studentID), PRIMARY KEY (classID)); CREATE TABLE student ( studentID int NOT NULL AUTO_INCREMENT, lastName varchar(255), firstName varchar(255), classID int, FOREIGN KEY (classID) REFERENCES class(classID), PRIMARY KEY (studentID)); ``` I am trying to ensure data consistency between the tables by using foreign key so that the DBMS can check for errors; however, it seems we can't do that for some reason. What's the error and is there an alternative? Also, when I fill a table that has a foreign key, I can't fill the field that's reserved for the foreign key(s), right? Also, is a foreign key considered to be a key at all?