SQL Server 2019 current version is 15.0.4223.1
Current version of Azure SQL is V12
Further, Azure SQL is "evergreen"
More companies are choosing Azure for their SQL workloads, and it is easy to see why. Azure SQL Database is evergreen, meaning it does not need to be patched or upgraded, and it has a strong track record of innovation and reliability for mission-critical workloads. But, in addition to delivering unparalleled innovation, it is also important to provide customers with the best price-performance. Here, once again, SQL Database comes out on top.
See more information about what evergreen means at https://azure.microsoft.com/en-ca/blog/azure-sql-database-continuous-innovation-and-limitless-scale-at-an-unbeatable-price/
Azure SQL is DaaS (Database-as-a-Service) where you don't need to patch the server vs. SQL Server 2019 typically runs on your server or on a Cloud IaaS (Infrastructure-as-a-Service) VM where you are in charge of managing your server.
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