Database Reference
In-Depth Information
Figure 12.9. A sample of data from the revised CLASS REGISTRATION view
There are three things to note about this view.
1.
The T
OTAL
S
TUDENTS
R
EGISTERED
field displays a single number for each class
name, which represents the total number of students registered for that class.
2.
The redundancy within the C
LASS
N
AME
field has been eliminated; all instances of
a given class name have been grouped into a single instance. As a result, C
LASS
N
AME
is now a
grouping field,
and its values cannot be modified in any way.
Note
All data fields in an aggregate view are grouping fields.
3.
Because an aggregate view is composed entirely of grouping fields and calculated
fields, you cannot modify any of its data.
Anaggregateviewismostusefulasthebasisofareportorasameansofprovidingvarious
types of statistical information. You'll learn later that you can apply filtering criteria to this
(or any) view in order to control and restrict the data that the view displays.
Validation View
A
validation view
issimilartoavalidationtableinthatitcanhelpimplementdataintegrity.
When a business rule limits a particular field's range of values, you can enforce the con-
