Question

I need help trying set-up Foreign Keys after having difficulty following Music library MySQL database. I have multiple tables: Albums, Songs, Genres, Music Videos, Solo, and Group. There are ids, names and other columns for each specific table. Each id is primary key with int(11). Solo and Group represent solo artists and groups. (soloID and groupID are the primary key for them)

Look again

It could be the way I set up my database.

Solo
•   djuIDs – int(11)
•   profilepic – varchar(255)
•   engname – varchar(255)
•   korname – varchar(255)
•   engbn – varchar(255)
•   occupation – set
•   recordlabel – varchar(255)
•   debut  - date
•   dateofbirth – date
•   officialsite -  varchar(255)
•   sitename –varchar(255)
•   page – varchar(255)
Group
•   djuIDs – int(11)
•   profilepic – varchar(255)
•   engname – text
•   korname – text
•   members – text
•   recordlabel – varchar(255)
•   debut – date
•   officialsite -  varchar(255)
•   sitename –varchar(255)
•   page – varchar(255)
Albums
•   albumID – int(11)
•   albumpic – varchar(255)
•   albumthpic – varchar(255)
•   albumTitle – varchar(255)
•   performer – varchar(255)
•   type – set (ex: ep, sp, studio)
•   titletrack – varchar(255)
•   genre
•   releasedate – date
•   distributor – varchar(255)
•   page – varchar(255)
Songs
•   songID – int(11)
•   albumpic – varchar(255)
•   tracknum – int(11)
•   songTitle – varchar(255)
•   performer – varchar(255)
•   album – varchar(255)
•   page – varchar(255)
Music Videos
•   mvID – int(11)
•   title – varchar(30)
•   mvpic – varchar(255)
•   performer – varchar(255)
•   album – varchar(255)
•   releasedate – date
•   vURL – varchar(255)
Genres
•   genreID – int(11)
•   genreName –varchar(30)
•   information – varchar(255)

Answer 1

I think that was one of my older answers… If you’ve used INT(11) as your primary keys, your foreign key definitions should look like something like the following table definitions for Artists and Albums:

CREATE TABLE Artists (
  /* will later be defined as a FK Albums.artistid */
  id INT NOT NULL PRIMARY KEY,
  name VARCHAR(1024) NOT NULL,
  description TEXT
) ENGINE=InnoDB;

CREATE TABLE Albums (
  id INT NOT NULL PRIMARY KEY,
  artistid INT NOT NULL,
  release_date DATETIME,
  genreid INT NOT NULL,
  picture BLOB,
  FOREIGN KEY (artistid) REFERENCES Artists (id),
  FOREIGN KEY (genreid) REFERENCES Genres (id)
)  ENGINE=InnoDB;

Since you have defined all your PK columns as INT(11), make sure that in the related tables you use the same data type. For example above, artistid INT NOT NULL assumes that the referenced column in Artists is defined as id INT NOT NULL.

In the definition above, I have made the FK columns as NOT NULL, but that isn’t strictly necessary. You could, for example, have an album with a NULL artist. If you think that’s a possibility, you should be able to omit the NOT NULL in the column definitions.