Welcome to the PostgreSQL Tutorial. The following few chapters are intended to give a simple introduction to PostgreSQL, relational database concepts, and the SQL language to those who are new to any one of these aspects. We only assume some general knowledge about how to use computers. No particular Unix or programming experience is required.

Most users at one time or another have dealt with hierarchical data in a SQL database and no doubt learned that the management of hierarchical data is not what a relational database is intended for. The tables of a relational database are not hierarchical (like XML), but are simply a flat list. Hierarchical data has a parent-child relationship that is not naturally represented in a relational database table.

Over the last couple of decades we've seen a growing gap between database-oriented software developers and in-memory application software developers. This leads to many disputes about how to use database features such as SQL and stored procedures. In this article I look at the question of whether to place business logic in SQL queries or in-memory code, considering primarily performance and maintainability based on an example of a simple, but rich SQL query.

Chess makes a fantastic game for programming examples. You will find hundreds of examples on the internet. Some dedicated to OO patterns, others to algorithms and so forth. Unfortunately, most of these examples do not use a database or if they do, treat the database as nothing more than a storage repository. In this series of articles we will use SQL Server and T-SQL to implement the game of chess with an emphasis on thinking in sets.

Developers are flocking to Ruby on Rails at an incredible pace. There's a great reason for this migration: Rails provides a robust framework built on one of the most flexible languages ever conceived. One of the tricks in the Rails bag is the concept of "Migrations." Migrations provide an excellent example of why developers would want to use the framework, and here's why: Generally speaking, managing changes to a database schema has been one of the most odious tasks for a team of developers. Most have relied on storing DDL in revision control, ever vigilant to ensure that our database creation scripts are updated and consistent with each rollout. That solution can be very clumsy in an Extreme Programming project. And because Rails encourages iterative development, it would be very easy to imagine the constant schema changes turning into nightmares. Fortunately, Migrations allows a developer to manage rollout, and rollback, of database schema changes in a controlled and consistent manner, and one that happens to feel very natural to a Rails programmer.

Ever wished for an easy way to transform SQL result sets into XML? It's a PEAR package named XML_Query2XML, and it provides a comprehensive framework to efficiently turn the results of a database query into a customizable XML document. This article introduces the package, and demonstrates useful real-world applications, including using it with XSL and XPath, combining it with data from external Web services, and creating database dump files.

The Oracle Berkeley DB team is frequently asked, "How do I do <SQL query here> in Berkeley DB?" So, this is an introduction to implementing much of your favorite SQL functionality in Oracle Berkeley DB. Not all SQL applications should be implemented in Oracle Berkeley DB--an open source, embeddable database engine that provides fast, reliable, local persistence with zero administration required--but if you have a relatively fixed set of queries and you care about performance, Berkeley DB may just be the way to go.

In this article you will learn some of the transferable concepts common to Oracle SQL, Linux operating system commands, and scripting. In particular, it will show how to use a "set oriented" way of thinking about problems that involve sets of data that need to be grouped, sorted, and filtered. These operations are familiar to those with a knowledge of SQL but are also often required when using Linux commands and or the Ruby programming language.

I will not an attempt to discuss mathematical set theory in any sort of rigorous disciplined fashion. Instead, all the fuzzy boundaries that exist in human language (and typical business problems) can be found throughout. Oracle SQL provides a much purer way of manipulating sets of data than scripting: each column contains fields of a defined type, and the logical data is handled independently of the underlying physical representation. Data returned from a query is not the same in any formal sense as the output of a shell command. The intent of what follows is pedagogical, to provide some analogies that are familiar to those who know SQL to leverage their problem solving abilities when required to work outside the database. It will provide a different perspective for approaching problems and encourage you to delve into new and unfamiliar areas.

In this article, the author delves into some commonly used ways of writing data access code and looks at the effect they can have on performance.

Ask the right questions before starting construction of your new PL/SQL-based application.