Beginning Microsoft SQL Server 2008 ... - S3 Tech Training

Chapter 8: Being Normal: Normalization and Other Basic Design Issues
❑ We were able to eliminate an instance of the information for ACME Co. That’s part of the purpose
of moving data that appears in repetitive groups — to just store it once. This both saves us space
and prevents conflicting values.
❑ We moved only repeating groups of data. We still see the same order date several times, but it
doesn’t really fit into a group — it’s just a relatively random piece of data that has no relevance
outside of this table.
So, we’ve dealt with our repeating data; next, we’re ready to move onto the second violation of first normal
form — atomicity. If you take a look at the ItemsOrdered column, you’ll see that there are actually
several different pieces of data there:
❑ Anywhere from one to many individual part numbers
❑ Quantity weight information on each of those parts
Part number, weight, and price are each atomic pieces of data if kept to themselves, but combined into
one lump grouping you no longer have atomicity.
Believe it or not, things were sometimes really done this way. At first glance, it seemed the easy thing to
do — paper invoices often had just one big block area for writing up what the customer wanted, and
computer-based systems were often just as close to a clone of paper as someone could make it.
We’ll go ahead and break things up — and, while we’re at it, we’ll add in a new piece of information in
the form of a unit price, as shown in Figure 8-1. The problem is that, once we break up this information,
our primary key no longer uniquely identifies our rows — our rows are still unique, but the primary key
is now inadequate.
Order No
(PK)
100
100
100
100
101
102
102
102
103
103
103
Figure 8-1
Order Date Customer No Part No Description Qty Unit Price Total Price Wt.
1/1/1999
1/1/1999
1/1/1999
1/1/1999
1/1/1999
1/1/1999
1/1/1999
1/1/1999
1/2/1999
1/2/1999
1/2/1999
54545
54545
54545
54545
12000
66651
66651
66651
54545
54545
54545
1A4536
0R2400
0R2403
4I5436
3X9567
8G9200
8G5437
3H6250
8G9200
2P5523
3X9567
Flange
Injector
Injector
Head
Pump
Fan
Fan
Control
Fan
Housing
Pump
For now, we’ll address this by adding a line item number to our table, as shown in Figure 8-2, so we can,
again, uniquely identify our rows.
5
4
4
1
1
7
1
1
40
1
1
15
27
29
750
62.50
12
15
32
12
165
42
75
108
116
750
62.50
84
15
32
480
165
42
6
.5
.5
3
5
3
3
5
3
1
5
221