Azure SQL Database offers a relational database in the cloud. It uses the last stable SQL Server on-premises database engine. Azure SQL Database can be used for a variety of applications, because it enables you to process both relational data and non-relational structures, such as graphs, JSON, spatial, and XML.

Azure SQL Database offers scalability, without causing any downtime for your databases. It offers column-based indexes, which make your queries perform much more quickly. There is built-in monitoring for your databases and built-in intelligence for increasing the performance of your database automatically, and it provides high availability, by providing automatic backups and point-in-time restores. You can also use active geo-replication, for global applications.

Azure SQL Database offers the following tiers for your databases:

• Elastic database pool: Elastic pools are a feature that helps in managing and scaling databases that have unpredictable usage demands. All databases in an elastic pool are deployed on the same database server and share the same resources. By managing the pool of databases and not the individual databases, they can share performance and scaling. The performance of this tier is expressed in elastic Database Transaction Units (eDTUs).
• Single database: This is a good fit if you have a database with predictable performance. Scaling is done for each database separately. The performance of this tier is expressed in Database Transaction Units (DTUs).
• Managed instance: This is a fully managed instance of the last stable SQL Server on-premises database engine. This option is most suitable for migrating on-premises SQL databases as-is to the cloud. It offers 100% compatibility with the latest SQL Server on-premises (Enterprise edition) database engine.