Choose a cloud SQL Server option: Azure Sql (PaaS) Database or SQL Server on Azure VMs (IaaS)

PaaS: Azure SQL Database
SQL Database, based on Microsoft SQL Server technologies.
MySQL Database, based on the ClearDB MySQL Database cloud service
Azure SQL Database architecture starts with an Azure subscription. Within the subscription, there is a resource group and within the resource group there are server instances and databases.

Azure SQL Database Architecture

Planning Azure SQL Databases

IaaS: SQL Server on Azure Virtual Machines

DocumentDB Databases
Azure DocumentDB is a NoSQL document database service designed from the ground up to natively support JSON and JavaScript directly inside the database engine. It’s an ideal and highly scalable solution for cloud apps that have predictable throughput, low latency, and flexible querying. With this system, you can implement rich queries over a schema-free JSON-based data model.