Table Relationships - Database Design for Mere Mortals - page 322

Figure 10.66. The relationship diagram for the EMPLOYEES and INVOICES tables
Now Zachary establishes the many-to-many relationship between the INVOICES and
PRODUCTS tables by creating a new linking table called INVOICE PRODUCTS. He
bases the new table on the I NVOICE N UMBER field from the INVOICES table and the
P RODUCT N UMBER field from the PRODUCTS table. Figure 10.67 shows the revised rela-
tionship diagram for the INVOICES and PRODUCTS tables.
Figure 10.67. Establishing and diagramming the many-to-many relationship between
the INVOICES and PRODUCTS tables
Zachary reviews each table structure to ensure that it conforms to the Elements ofthe Ideal
Table.Fortunately,hedoesn'thavetomakeanymodificationsbecauseallofthetablestruc-
tures are sound. He now refines the foreign keys in each table by making certain that each
one complies with the Elements of a Foreign Key. Finally, Zachary modifies the appro-
priate items in the General Elements and Logical Elements sections of each foreign key's
Field Specifications sheet. Figure 10.68 shows the modifications he's made for one of the
foreign keys. (I've highlighted the changes so that you can recognize them more easily.)