SQL Series....01

SQL (short for structured query language) is an industry-standard language specifically designed to enable people to create databases, add new data

to databases, maintain the data, and retrieve selected parts of the data. Various kinds of databases exist, each adhering to a different conceptual model. SQL was originally developed to operate on data in databases that follow the relational model. Recently, the international SQL standard has incorporated part of the object model, resulting in hybrid structures called object-relational databases. In this article, I discuss data storage, devote a section to how the relational model compares with other major models, and provide a look at the important features of relational databases.

Before I talk about SQL, however, first things first: I need to nail down what I mean by the term database. Its meaning has changed as computers have changed the way people record and maintain information.

Keeping Track of Things

Today, people use computers to perform many tasks formerly done with other tools. Computers have replaced typewriters for creating and modifying documents. They’ve surpassed electromechanical calculators as the best

way to do math. They’ve also replaced millions of pieces of paper, file folders, and file cabinets as the principal storage medium for important information. Compared to those old tools, of course, computers do much more, much faster — and with greater accuracy. These increased benefits do come at a cost, however. Computer users no longer have direct physical access to their data.

When computers occasionally fail, office workers may wonder whether com-puterization really improved anything at all. In the old days, a manila file folder only “crashed” if you dropped it — then you merely knelt down, picked up the papers, and put them back in the folder. Barring earthquakes or other major disasters, file cabinets never “went down,” and they never gave you an error message. A hard drive crash is another matter entirely: You can’t “pick up” lost bits and bytes. Mechanical, electrical, and human failures can make your data go away into the Great Beyond, never to return.

Taking the necessary precautions to protect yourself from accidental data loss allows you to start cashing in on the greater speed and accuracy that computers provide.

If you’re storing important data, you have four main concerns:

Storing data needs to be quick and easy, because you’re likely to do it often.

The storage medium must be reliable. You don’t want to come back later and find some (or all) of your data missing.

Data retrieval needs to be quick and easy, regardless of how many items you store.

You need an easy way to separate the exact information that you want from the tons of data that you don’t want.

State-of-the-art computer databases satisfy these four criteria. If you store more than a dozen or so data items, you probably want to store those items in a database.