SQL Database is an Azure V12 SQL database running within the SQL Server platform service and associated with a logical server. An Azure V12 SQL database is similar in most respects to a SQL Server 2016 database, but there are a few differences. The SQL Server platform service provides the functionality to create and manage your database solution, freeing you up to focus on the solution rather than the underlying network, storage, and compute resources in addition to the SQL Server instance.
When creating your SQL database, you specify the amount of resources available to your new SQL database and associate it with either a new or an existing SQL Database logical server. The features and resource limits available to your new SQL database are determined by the service tier and performance level you select for the SQL database. The SQL Database service manages the resources available to each SQL database using a resource governance mechanism and hard resource limits (both of which are discussed below). A SQL database is portable and can be moved between logical servers.
To secure your SQL Database logical server and database instances, a SQL Database firewall limits connectivity to either Azure services or specific IP addresses. The SQL Database firewall operates at both the logical server and the database level.
Source of Information : Migrating SQL Server Databases to Azure