Microsoft Azure SQL Subscriptions - Monthly PAYG or Annual Plans

Azure SQL is a family of managed, secure, and intelligent products that use the SQL Server database engine in the Azure cloud. Azure SQL Database: Support modern cloud applications on an intelligent, managed database service, that includes serverless compute.

Microsoft Azure SQL Edge Subscription
The Microsoft Azure SQL Edge Subscription is a per device licence
Azure SQL Edge is an optimised relational database engine geared for IoT and IoT Edge deployments. It provides capabilities to create a high-performance data storage and processing layer for IoT applications and solutions. Azure SQL Edge provides capabilities to stream, process, and analyse relational and non-relational such as JSON, graph and time-series data, which makes it the right choice for a variety of modern IoT applications.

Azure SQL Edge is built on the latest versions of the SQL Server Database Engine, which provides industry-leading performance, security and query processing capabilities. Since Azure SQL Edge is built on the same engine as SQL Server and Azure SQL, it provides the same Transact-SQL (T-SQL) programming surface area that makes development of applications or solutions easier and faster, and makes application portability between IoT Edge devices, data centers and the cloud straight forward.

What is Azure SQL Edge video on Channel 9:
Microsoft Azure SQL Edge - 3 Year Subscription
Azure SQL Edge per device for 3 Years Subscription