Database Reference
In-Depth Information
helpthoseofyouusingquery-buildingtoolstounderstandandtroubleshootthequeriesyou
create with these tools, and it will definitely be to your advantage should you need to work
with high-end database software programs, such as Oracle and Microsoft SQL Server.
Note
Although a detailed discussion of SQL is beyond the scope of this topic, you
shouldunderstandthatSQLisalanguagedirectlyrelatedtotherelationaldatabase
model. If you have a desire or need to study SQL, you could start by reading my
second topic,
SQL Queries for Mere Mortals
®
,
Second Edition,
and then move on
to any of the other SQL topics that I have listed in
Appendix H
,
“
Recommended
Advantages of a Relational Database
Therelationaldatabaseprovidesanumberofadvantagesoverpreviousmodels,suchasthe
following.
•
Built-in multilevel integrity:
Data integrity is built into the model at the field level
to ensure the accuracy of the data; at the table level to ensure that records are not
duplicated and to detect missing primary key values; at the relationship level to en-
sure that the relationship between a pair of tables is valid; and at the business level
to ensure that the data is accurate in terms of the business itself. (Integrity is dis-
cussed in detail as the design process unfolds.)
•
Logical and physical data independence from database applications:
Neither
changes a user makes to the logical design of the database, nor changes a database
software vendor makes to the physical implementation of the database, will ad-
versely affect the applications built upon it.
•
Guaranteed data consistency and accuracy:
Data is consistent and accurate due to
the various levels of integrity you can impose within the database. (This will be-
come quite clear as you work through the design process.)
•
Easy data retrieval:
At the user's command, data can be retrieved either from a
particular table or from any number of related tables within the database. This en-
ables a user to view information in an almost unlimited number of ways.
These and other advantages have proved beneficial to the business community and to all
those who need to collect and manage data. Indeed, the relational database has become the
database of choice in many circumstances.
One commonly perceived disadvantage of the relational database was that software pro-
grams based on it ran very slowly. This was not a fault of the relational model itself, but
