Beginning SQL

Appendix A
376
Figure A-1
ISBN is a unique reference that identifies books and makes up part of the primary key. BookSellerId
uniquely identifies a bookseller and provides the second part of the primary key. Finally, PublisherCode
is the third part of the primary key for Table1. For the WrittenBy table, the primary key is the ISBN and
AuthorId. In Authors, the AuthorId is the primary key, a newly created column that Table1 references.
So far, the database is roughly in first normal form. Second normal form specifies that no partial dependencies
can exist between any of the columns on the primary key. In Table1, BookTitle and
YearPublished are dependent on ISBN but not dependent on BookSellerId or PublisherCode.
BookSellerName and BookSellerTelNo are dependent only on the BookSellerId and not on any of the
other parts of the primary key. Finally, PublisherCode determines PublisherName and
PublisherAddress, but no dependency exists between any of the other parts of the primary key.
Therefore, in order to make the table comply with second normal form, the three independent parts
need to be split up into three tables, which you can call something like Books, BookSellers, and
Publishers. Figure A-2 illustrates how this might look: