Stephane Faroult - The art of SQL

Copyright 2008 O'Reilly Media, Inc.

There are three main types of SQL books: books that teach the logic and the syntax of a particular SQL dialect, books that teach advanced techniques and take a problem-solving approach, and performance and tuning books that target experts and senior DBAs. On one hand, books show how to write SQL code. On the other hand, they show how to diagnose and fix SQL code that has been badly written. I have tried, in this book, to teach people who are no longer novices how to write good SQL code from the start and, most importantly, to have a view of SQL code that goes beyond individual SQL statements.

Teaching how to use a language is difficult enough; but how can one teach how to efficiently use a language? SQL is a language that can look deceivingly simple once you have been initiated. And yet it allows for an almost infinite number of cases and combinations. The first comparison that occurred to me was the game of chess, but it suddenly dawned on me that chess was invented to teach war. I have a natural tendency to consider every new performance challenge as a battle to be fought against an army of rows, and I realized that the problem of teaching developers how to use databases efficiently was similar to the problem of teaching officers how to conduct a war. You need knowledge, you need skills, and you need talent. Talent cannot be taught, but it can be nurtured. This is what most strategists, from Sun Tzu, who wrote his Art of War 25 centuries ago, to modern-day generals, have believedso they tried to pass on the experience acquired on the field through simple maxims and rules that they hoped would serve as guiding stars among the sound and fury of battles. I have tried to apply this method to more peaceful aims, and I have mostly followed the same plan as Sun Tzuand I've borrowed his title. Many respected IT specialists claim the status of scientists; "Art" seems to me more appropriate than "Science" when it comes to defining an activity that requires flair, experience, and creativity, as much as rigor and understanding.[] It is quite likely that my fondness for Art will be frowned upon by some partisans of Science, who claim that for each SQL problem, there is one optimal solution, which can be attained by rigorous analysis and a good knowledge of data. However, I don't see the two positions at odds. Rigor and a scientific approach will help you out of one problem at one given moment . In SQL development, if you don't have the uncertainties linked to the next move of the adversary, the big uncertainties lie in future evolutions. What if, rather unexpectedly, the volume of this or that table increases? What if, following a merger, the number of users doubles? What if we want to keep several years of data online? How will a program behave on hardware totally different from what we have now? Some architectural choices are gambles on the future. You will certainly need rigor and a very sound theoretical knowledgebut those qualities are prerequisites of any art. Ferdinand Foch, the future Supreme Commander of the Allied armies of WWI, remarked at a lecture at the French Ecole Suprieure de Guerre in 1900 that:

The art of war, like all other arts, has its theory, its principlesotherwise, it wouldn't be an art.

This book is not a cookbook, listing problems and giving "recipes." The aim is much more to help developersand their managersto raise good questions. You may well still write awful, costly queries after having read and digested this book. One sometimes has to. But, hopefully, it will be knowingly and with good reason.