• Datacenter: SQL Server 2008 R2 Datacenter is the full-featured edition of SQL server and is designed for datacenters that need the high levels of application support and scalability.

• Enterprise: SQL Server Enterprise Edition includes both the core database engine and add-on services, with a range of tools for creating and managing a SQL Server cluster.

• Standard: SQL Server 2008 R2 edition includes the core database engine, along with the stand-alone services.

• Web: SQL Server Web Edition is a low cost option for web hosting applications.

• Workgroup: SQL Server Workgroup Edition includes the core database functionality but does not include the additional services.

• Express: SQL Server Express Edition is a scaled down, free edition of SQL Server, which includes the core database engine. This is the free version.

• Other specialized Editions include SQL Azure, Developer and Compact, Parallel Data Warehouse.

In summary, the main difference between SQL Server Datacenter and Enterprise other than the price is the fact that DC can support more processors.

• SQL DC version can run as many processors as the operating system is capable of running. If running on Windows 2008 Server Datacentre edition, this is 64 processors. Enterprise SQL server can run on a maximum of 8 processors.

• Regarding memory, SQL Server DC can run as much RAM as the Operating System, which is 2TB if installed on Datacentre or Enterprise. However the Enterprise version will also allow up to 2TB of RAM.

• As of Oct 2011, DC version costs about double the price of the Ent version.

For prices please see the table below.

There are big differences in CPU and RAM scalability between Enterprise SQL Server and SQL Server Standard.

• Enterprise will run up to 8 processors, Standard will run up to 4 processors.

• Enterprise will run up to 2TB of RAM whereas Standard will run 64GB of RAM.

• SQL Server Enterprise Edition includes both the core database engine and add-on services, with a range of tools for creating and managing a SQL Server cluster, which are not included with Standard.

• SQL Server Standard has much reduced ability to cluster. SQL Server Enterprise allows for 16 nodes in a cluster, whereas it is only 2 with SQL Standard.

• With SQL server standard it is only possible to mirror databases with single threading and in synchronous mode only.

If you are working with large volumes of data you should choose Enterprise/ Data center edition. Enterprise offers table partitioning, parallel indexing, and indexed views that can significantly improve performance in large environments.

If you are working in a high-availability, mission-critical environment, you probably need Enterprise or Datacenter edition. Online indexing will allow you to maintain indexes without scheduling down-time, and Online Restore and Fast Recovery are both options you want when recovering from a failure.

Note that when setting up a SQL mirror or Cluster, you need the Enterprise Windows Server operating system. This is because it uses the Windows clustering service.

SQL Server Standard is ideally suited for the following usage scenarios:

• Departmental deployments

• Small to medium scale OLTP deployments

• OLTP deployments that are not expected to rapidly grow in the future

• Reporting and analysis deployments

For prices please see the table below.

• With SQL Server Standard it is possible to cluster 2 servers in a mirror. With Web, it is only possible to have a second server as a witness. The role of the witness server is to recognise whether an automatic failover is required. This means that you can use a SQL Web edition server as a witness server, but can't set up a mirror with SQL Web Edition servers only.

• SQL Server 2008 Web Edition helps hosters to provide low cost highly scalable hosting with a low monthly licensing price, four CPU support, and no limits on memory and database size for increased scalability. SQL Server 2008 Web Edition also supports the new improved SQL Server Driver for PHP, enabling reliable, scalable integration with SQL Server for PHP applications deployed on the Windows platform.

• SQL Server 2008 Web Edition may not be used to support line of business applications (e.g. Customer Relationship Management, Enterprise Resource Management and other similar applications).Therefore, if additional capabilities are needed, you should consider using one of the other editions of SQL Server 2008 (e.g. Standard or Enterprise).

For prices please see the table below.

SQL Server Express Edition is a scaled down, free edition of SQL Server, which includes the core database engine.

SQL Management Studio Express is available as a separate free download from Microsoft to manage SQL Express.

Other specialized Editions include SQL Azure, Developer and Compact, Parallel Data Warehouse. For completeness a summary for each is as below:

• SQL Azure (was formerly called SQL Server Data Services and later SQL Services) is a cloud-based service from Microsoft offering data storage capabilities as a part of the Azure Services Platform. Unlike similar cloud-based databases, SQL Azure allows relational queries to be made against stored data, which can either be structured or semi-structured, or even unstructured documents. SQL Azure features querying data, search, data analysis and data synchronization. SQL Azure uses Microsoft SQL Server as a backend, but it exposes only a few data types - including string, numeric, date and Boolean and uses an XML-based format for data transfer

• Microsoft SQL Server 2008 R2 Developer edition has all the features of the Datacenter Edition but is licensed only for development, test, and demo use.

• Microsoft SQL Server 2008 R2 Parallel Data Warehouse is a scalable data warehouse product from Microsoft that delivers performance and scalability through parallel processing. SQL Server PDW uses SQL Server 2008 R2 databases for distributed processing and data storage. The appliance partitions large database tables across multiple physical nodes, with each node running its own instance of SQL Server 2008 R2. When a report connects to SQL Server PDW to retrieve report data, it connects to the control node, which manages query processing, in the SQL Server PDW appliance. After the connection is made, there are no differences between working with an instance of SQL Server that is and is not within a SQL Server PDW environment.

• Microsoft SQL Server Compact (SQL CE) is a compact relational database produced by Microsoft for applications that run on mobile devices and desktops. Prior to the introduction of the desktop platform, it was known as SQL Server for Windows CE and SQL Server Mobile Edition. The latest release is the SQL Server Compact It is free to download and redistribute.