MySQL FOREIGN KEY error, ON DELETE CASCADE

Question

I have absolutely no clue why MySQL is having an issue with the second CREATE TABLE statement.

CREATE TABLE User(
    uid INTEGER, 
    url CHAR(100),
    firstname CHAR(40),
    lastname CHAR(40),
    PRIMARY KEY(uid)
);

The below is the one that causes problems:

CREATE TABLE Follows(
    uid INTEGER,
    url CHAR(100),
    PRIMARY KEY(uid,url),
    FOREIGN KEY(uid) REFERENCES User(uid), ON DELETE CASCADE,
    FOREIGN KEY(url) REFERENCES User(url), ON DELETE CASCADE
    );

Error I get is:

#1064 - You have an error in your SQL syntax; check the manual that corresponds to your MySQL server version for the right syntax to use near 'ON DELETE CASCADE, FOREIGN KEY(url) REFERENCES User(url), ON DELETE CASCADE)' at line 1

Answer 1

There are a few issues here:

First the on delete cascade is part of the foreign key definition, so the comma ( , ) before it should be removed.

Second, the second foreign key references url , which is not a unique key, and therefore is not allowed. So either remove this constraints:

CREATE TABLE Follows (
    uid INTEGER,  
    url CHAR(100),  
    PRIMARY KEY(uid,url),  
    FOREIGN KEY(uid) REFERENCES User(uid) ON DELETE CASCADE
);

Or define another unique key on url :

CREATE TABLE User(
    uid INTEGER, 
    url CHAR(100),
    firstname CHAR(40),
    lastname CHAR(40),
    PRIMARY KEY(uid),
    UNIQUE (url)
);


CREATE TABLE Follows (
    uid INTEGER,  
    url CHAR(100),  
    PRIMARY KEY(uid,url),  
    FOREIGN KEY(uid) REFERENCES User(uid) ON DELETE CASCADE,
    FOREIGN KEY(url) REFERENCES User(url) ON DELETE CASCADE
);

Answer 2

尝试在引用用户（uid）和引用用户（url）之后删除此“，”

Answer 3

you have to put a gap after User(uid) ON DELETE CASCADE, also you should write in to the end of the query like this: engine='innodb';

i mean between the last ) and ;