CODEWITHSUNDEEP
mysql
bruhhhhh
bruhhhhh

Reputation: 121

Why am I getting "Cannot add foreign key constraint" error with the following sql command?

I am getting an error while running the following commands on a MySQL server. 

CREATE TABLE users (
    userID INT NOT NULL AUTO_INCREMENT,
    PRIMARY KEY(userID),
    firstname VARCHAR(100) NOT NULL,
    lastname VARCHAR(100) NOT NULL,
    username VARCHAR(120) NOT NULL UNIQUE,
    hashpass VARCHAR(100) NOT NULL
) ENGINE=INNODB ;


CREATE TABLE posts (
    postID INT AUTO_INCREMENT,
    text VARCHAR(1000),
    imageURI VARCHAR(100),
    userID VARCHAR(120) NOT NULL, 

    PRIMARY KEY(postID),

    FOREIGN KEY (userID)
    REFERENCES users (userID)
    ON DELETE CASCADE,

    tags VARCHAR(500)
) ENGINE=INNODB;

I am getting the following error: 

Cannot add foreign key constraint

Upvotes: 1

Views: 62

Answers (2)

Rahul Tripathi
Rahul Tripathi

Reputation: 172448

Try to use the same type of your primary keys - users.userID int - on the foreign keys - posts.userID - as well.

WORKING SQL FIDDLE

Try like this:

CREATE TABLE users (
userID INT NOT NULL AUTO_INCREMENT,
PRIMARY KEY(userID),
firstname VARCHAR(100) NOT NULL,
lastname VARCHAR(100) NOT NULL,
username VARCHAR(120) NOT NULL UNIQUE,
hashpass VARCHAR(100) NOT NULL
) ENGINE=INNODB ;


CREATE TABLE posts (

postID INT AUTO_INCREMENT,
text VARCHAR(1000),
imageURI VARCHAR(100),
userID INT NOT NULL,     <---Change here

PRIMARY KEY(postID),

FOREIGN KEY (userID)
REFERENCES users (userID)
ON DELETE CASCADE,

tags VARCHAR(500)
) ENGINE=INNODB;

Upvotes: 1

Yu Yenkan
Yu Yenkan

Reputation: 765

your foreign key

userID VARCHAR(120) NOT NULL,

is different with

userID INT NOT NULL AUTO_INCREMENT,

Upvotes: 0

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