Database Reference
In-Depth Information
Figure 10.14. Diagramming a many-to-many relationship
In this case, there is a crow's foot symbol located next to
each
table.
Figure 10.15
shows
the relationship diagram for the STUDENTS and CLASSES tables in
Figure 10.13
.
Figure 10.15. The relationship diagram for the STUDENTS and CLASSES tables
Problems with Many-to-Many Relationships
A many-to-many relationship has an inherent peculiarity that you must address before you
can effectively use the data from the tables involved in the relationship. The issue is this:
How do you
easily
associate records from the first table with records in the second table in
order to establish the relationship? This is an important question because you'll encounter
problems such as these if you do not establish the relationship properly.
• It will be tedious and somewhat difficult to retrieve information from one of the
tables.
• One of the tables will contain a large amount of redundant data.
• Duplicate data will exist within both tables.
