SQL Azure is a relational database service that operates in “the cloud”. It is based on Microsoft SQL Server and is hosted on servers in Microsoft’s data centres.
Is SQL Azure the same as SQL Server? Well, yes and no. It is similar in that you have a virtual SQL Server instance which operates very much like a physical instance, but which is administered differently. For example, whilst you can create and manage databases, users and logins, you have no control over the physical environment such as the location of data files and logs.
Features Not Currently Supported
SQL Azure does not yet support all of the features found in SQL Server, though it has been hinted that more features will gradually be added in future. At the moment, SQL Azure does not contain:
- Analysis Services
- Reporting Services
- Service Broker
- Database Mirroring
Note: Replication is not supported, either, but since SQL Azure automatically replicates and load balances in order to provide a high-availability service, this seems fairly irrelevant.
Other Differences
SQL Azure supports most of the data types you would find in SQL Server 2008, but not all. For example, the new spatial and geometry types are not supported. A full list can be found in this MSDN article. Other features that are currently missing include:
- Common-language runtime
- Multiple active result sets (MARS)
- Linked servers/distributed queries
Despite the differences, there are certainly enough features to cater for the vast majority of line-of-business applications.
A more complete overview can be found on this MSDN page.