SQL Azure is Microsoft’s cloud database service. Based on SQL Server database technology and built on Microsoft’s Windows Azure cloud computing platform, SQL Azure enables organizations to store relational data in the cloud and quickly scale the size of their databases up or down as business needs change. Data is hosted, managed and provisioned in Microsoft data centers.
Organizations can build applications on-premises and move them to SQL Azure or build them on Windows Azure and keep the data in the cloud. SQL Azure supports SQL Server’s Transact-SQL (T-SQL) query language, offers built-in support for high availability and fault tolerance and allows for data to be synchronized between on-premises SQL Server and cloud databases.
Database analysts have pointed out a few important differences between SQL Azure and SQL Server. For example, SQL Azure doesn’t support all T-SQL commands, SQL Server data types like XML or functions such as cross-database joins, and the maximum database size currently is just 50 GB. The current release also does not perform scheduled backups and restores, though Microsoft has said this will be addressed in future releases.