But if you have an extensive collection of Peter Gabriel albums, you'd end up with a lot of redundancy in your database. You can imagine the progression from here, especially for a large database of music like an e-commerce site. Any time you have to re-enter data, you're likely to enter it incorrectly. In addition, redundant data takes up extra space in the database. And that's the whole essence of relational databases.
Relationships are all about reducing database redundancy.
We can take the record for Peter Gabriel and break it into a separate table. Now that we have the information about the artist separated from the album information, we can redesign the table of information for the CDs themselves. I've highlighted the column where the ArtistName string was replaced with a primary key from the table containing the related data record. In database parlance, this is typically called a foreign key . The two database tables are now related by the ArtistID key field.