errno 150 mySQL foreign key

Question

This SQL is giving me Errno 150 when i'm trying to create the second table with the foreign key on UserID

Can anyone please advice me what am i doing wrong?

CREATE DATABASE IF NOT EXISTS  OTA;
USE OTA;
CREATE TABLE IF NOT EXISTS Users
(
UserID int AUTO_INCREMENT NOT NULL PRIMARY KEY,
UserName varchar(255) NOT NULL,
Email varchar(255) UNIQUE ,
PW varchar(255),
PN varchar(255),
Admin BIT
);


CREATE TABLE IF NOT EXISTS Notes
(
UID int AUTO_INCREMENT NOT NULL PRIMARY KEY,
Note varchar (255) NOT NULL,
c_Date Date NOT NULL,
c_text varchar (255) NOT NULL,
FOREIGN KEY (UID) REFERENCES Persons(UserID)
);

Sorry for being a duplicate question but i can't find my answer between the related ones.

Answer 1

The problem is that you are trying to reference Persons(UserID) when your first table is called Users . Try this for your key:

FOREIGN KEY (UID) REFERENCES Users(UserID)

However, you should have a separate column for the note ID.

Answer 2

Try declaring the primary key after:

CREATE TABLE Orders
(O_Id int NOT NULL,
OrderNo int NOT NULL,
P_Id int,
PRIMARY KEY (O_Id),
FOREIGN KEY (P_Id) REFERENCES Persons(P_Id))

Also, you auto-incremented both UID and UserID. This is fine if they are the same length, but if you try to reference a foreign key value that doesn't exist, you will get an error.