Competition in the Express database market is at an all-time high. Following Microsoft's lead with SQL Server 2005 Express Edition, Oracle and IBM have both released Express versions of their enterprise-oriented databases. Oracle’s lightweight database is called Oracle 10g Express Edition (Oracle Database XE), and IBM's offering is called DB2 Express-C. In addition to the entry of these two giants into the lightweight-database arena, the venerable open-source MySQL database is also a formidable contender for entry-level databases. You can choose between two MySQL products: MySQL Community Server, which is the free open-source product, and MySQL Enterprise, which is a "for sale" product. At first glance, it might seem difficult to tell these products apart because they have many features in common. Your best choice will depend on the features that differentiate them, your target platform, and the tools you use to develop your applications.

All of the entry-level databases I’ve mentioned are essentially free, and they all provide the same type of relational-database services. They are also similar in the level of scalability that they offer. The supported OS, memory, and storage capacity are the first places you’ll see differences. SQL Server Express runs only on the Windows OS and it supports one CPU, 1GB of RAM, and multiple 4GB databases. Oracle Database XE runs on Windows and Linux OSs, and it supports 1 CPU, 1GB of RAM, and an overall total of 4GB of user data (but not multiple 4GB databases). DB2 Express-C also runs on Windows and Linux, and it provides a bit more scalability because it can run on systems that have up to 2 CPUs, supports 4GB of RAM, and has no database storage size restrictions. MySQL Community Server runs on Windows and Linux, and it doesn’t have any limit on RAM or storage.

Each of these products has its strengths. SQL Server Express provides high levels of performance and deep CLR and XML integration. If, like most developers, you're using Microsoft .NET technologies and you're developing for the Windows platform that makes up the bulk of the desktop market, SQL Server Express a great choice because its integration with the Visual Studio 2005 development product is unequaled. The SQL Server Express Advanced Edition also includes the SQL Server Management Studio Express (SSMSE) management GUI and support for Reporting Services, a component that has no equivalent in the other lightweight database products. For Oracle, there's a bundled set of Web-application development tools. DB2 Express-C offers greater scalability than the other lightweight databases on the market, a built-in management GUI, and XML integration. MySQL Community Server is a small-footprint, high-performance database.

The bottom line is that all of these products are capable, and the best choice typically depends on multiple factors. Naturally, if you're looking for Linux support, SQL Server Express isn’t your choice. MySQL is the usual database of choice for Linux applications because it’s an open-source product. But if you’re developing applications and supporting users in a Windows environment, SQL Server Express offers powerful reporting capabilities and unparalleled integration with the Visual Studio development environment.