MySQL Creating tables with Foreign Keys giving errno: 150

Question

I am trying to create a table in MySQL with two foreign keys, which reference the primary keys in 2 other tables, but I am getting an errno: 150 error and it will not create

Answer 1

Definitely it is not the case but I found this mistake pretty common and unobvious. The target of a FOREIGN KEY could be not PRIMARY KEY. Te answer which become useful for me is:

A FOREIGN KEY always must be pointed to a PRIMARY KEY true field of other table.

CREATE TABLE users(
   id INT AUTO_INCREMENT PRIMARY KEY,
   username VARCHAR(40));

CREATE TABLE userroles(
   id INT AUTO_INCREMENT PRIMARY KEY,
   user_id INT NOT NULL,
   FOREIGN KEY(user_id) REFERENCES users(id));