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The Art of SQL 225

Graeme Williams writes "One difference between SQL and a conventional procedural programming language is that for SQL there's a bigger gap between what the code says and what the code does. The Art of SQL is the opposite of a cookbook – or rather it's about cooking rather than recipes. It's not a reference manual, although there's plenty to refer back to. It's an intermediate level book which assumes you know how to read and write SQL, and analyzes what SQL does and how it does it." Read on for Graeme's review.
The Art of SQL
author Stéphane Faroult with Peter Robson
pages xvi + 349
publisher O'Reilly Media
rating 9
reviewer Graeme Williams
ISBN 0-596-00894-5
summary An excellent way to improve your approach to SQL

I guess it's normal for an intermediate text to present a number of serious examples, the idea being that the code from an example can be applied to roughly similar problems with roughly similar solutions. I think Faroult's goal is both more abstract and more ambitious. He wants to expand your ability to navigate among and analyze alternative SQL statements with more confidence and over a larger range. This isn't so much a book about SQL as it is about thinking about SQL.

There's almost no chance that the SQL examples in the book will be directly applied to a real problem. The examples are relevant at one remove: What does thinking about this example tell me about thinking about my current problem? So the book doesn't come with downloadable samples. There's no point.

The first few chapters of the book lay a foundation for the rest. As each brick in this foundation is placed, it sometimes feels as though it's placed firmly on your head. Think about indexes ... whack! Think about join conditions ... whack! These chapters have very few examples – the goal is to force you to think through queries from first principles. It's more effective (and less painful) than it sounds.

These introductory chapters cover how a query is constructed and executed, including how a query optimizer uses the information which is available to it. Faroult discusses the costs and benefits of indexes, and the interaction of physical layout with indexes, grouping, row ordering and partitioning. He also explains the difference between a purely relational query and one with non-relational parts, and how such a query can be analyzed in layers. Chapter 4 is available on the book's web page. It will give you a good idea of the style of the book, but not of the level of SQL discussed – the longest example in the chapter is just 15 lines.

Chapter 6 presents and analyzes nine SQL patterns, from small result sets taken from a few tables, to large result sets taken from many tables. The chapter falls roughly in the middle of the book, and feels like its heart. Prior chapters have built up to this one, and subsequent chapters are elaborations on particular topics. The theme of the book, to the extent that it has one, is that details matter. Different SQL statements can be used to produce the same result, but their performance will be different depending on details of the data and database. A change to the database structure, such as adding an index, might improve performance in one set of circumstances, but make it worse in another. The case analysis in this chapter will make you more sensitive to details in query design and execution.

The authors almost never mention particular database products. Their justification is that any absolute statement would be invalidated by the next release, or even a different hardware configuration, and anyway, that's not the business they're in. But sometimes this can go too far. The phrase "A clever optimizer ... will be able to" is too hypothetical by half. Is this an existing hypothetical query optimizer, or a vision of a future optimizer? Or the optimizer of one hypothetical database product and not of another? I suspect that Faroult knows and is simply being coy. It's just unhelpful not to tell us what existing databases will do, even if depends on the release or the hardware.

Faroult does this because he's not much interested in telling you what actually happens when a particular SQL statement is executed by a particular database. If the authors wanted a cute title for the book, I'm surprised they passed over The Zen of SQL Maintenance. When you look at an SQL statement, Faroult wants you to see what other SQL statements would do under other circumstances. He literally wants you to see the possibilities.

The second half of the book continues the analysis of chapter 6 into special cases, such as OLAP and large volumes of data, monitoring and resolving performance issues, and debugging problematic SQL.

Chapter 7 discusses tree-structured data, like an employee table with a column for the employee's manager. Faroult likes his own solution best, but presents an alternative approach by Joe Celko clearly enough for you to explore that as well.

Chapter 8 includes a series of examples of SQL and PHP. For anyone like me who spends more time in various programming languages than in SQL, this chapter is a small gem. It nicely illuminates the care needed in deciding what happens in code and what happens in SQL.

Chapter 9 addresses locking and concurrency, as it applies to both physical and logical parallelism. Transactions are included, but the discussion is just one part of a 20-page chapter and seems thin.

The Art of SQL is very clearly written. Whether it is "easy" will depend on how comfortable you are with SQL. This book is targeted at (page xi) "developers with significant (one year or, preferably, more) experience of development with an SQL database", their managers and software architects. I have months of experience spread over a decade or more, so I'm nominally outside the target audience. I found the SQL examples and discussion clear once I had a chance to let them sink in. If you're working with SQL regularly, they'll be perfectly clear.

The graphs let down the otherwise high quality of the book. For example, Figure 5-3 shows a rate (higher is better) but the legend says "Relative cost" (higher is worse). Figures 9-1 through 9-3 on facing pages 228 and 229 show response time histograms for three different query rates but don't show what the rates are. The x-axis of Figure 10-1 seems to be calendar time, but it's decorated with a stop watch icon. And as a representative of rapidly aging boomers with rapidly deteriorating eyesight, could I beg book designers not to put figure legends in a smaller font than the text of the book? Diagrams should be simple and clear, not something to puzzle over.

This is a book to conjure with, but it's not a book for everyone. Some people may find it too abstract, with too much discussion of too few examples. If you're completely new to SQL, the book will be hard going. If you have very many years of experience with SQL, it's just possible that you won't find anything new in the book, although I expect you'll find a lot to think about. For anyone in between, The Art of SQL is a excellent way to improve the way you attack problems in database and query design.

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The Art of SQL

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