PHP and MySQL Web Development 4th Ed-tqw-_darksiderg

214 Chapter 8 Designing Your Web Database
Use Atomic Column Values
Using atomic column values means that in each attribute in each row, you store only
one thing. For example, you need to know what books make up each order.You could
do this in several ways.
One solution would be to add a column to the Orders table listing all the books that
have been ordered, as shown in Figure 8.5.
ORDERS
OrderID
CustomerID
Amount
Date
Books Ordered
1
3
27.50
02-Apr-2007
0-672-31697-8
2
1
12.99
15-Apr-2007
0-672-31745-1. 0-672-31509-2
3
2
74.00
19-Apr-2007
0-672-31697-8
4
3
6.99
01-May-2007
0-672-31745-1. 0-672-31509-2. 0-672-31697-8
Figure 8.5
With this design, the Books Ordered attribute in each row has
multiple values.
This solution isn’t a good idea for a few reasons.What you’re really doing is nesting a
whole table inside one column—a table that relates orders to books.When you set up
your columns this way, it becomes more difficult to answer such questions as “How
many copies of Java 2 for Professional Developers have been ordered?”The system can no
longer just count the matching fields. Instead, it has to parse each attribute value to see
whether it contains a match anywhere inside it.
Because you’re really creating a table-inside-a-table, you should really just create that
new table.This new table, called Order_Items, is shown in Figure 8.6.
ORDER_ITEMS
OrderID
ISBN
Quantity
1
2
2
3
4
4
4
0-672-31697-8
0-672-31745-1
0-672-31509-2
0-672-31697-8
0-672-31745-1
0-672-31509-2
0-672-31697-8
1
2
1
1
1
2
1
Figure 8.6
This design makes it easier to search for particular books that
have been ordered.