Compatibility Level Drift When Migrating SQL Server 2019 to Azure SQL Database

Determine the appropriate compatibility level for a SQL Server 2019 database being migrated to Azure SQL Database (single database or managed instance) so that existing query behavior is preserved while evaluating access to newer features supported by the service.

The migration introduces uncertainty because changing the compatibility level can alter query plans and performance in ways that are not easily reversed, the default level applied to newly created Azure databases may differ from the source level, older levels are subject to deprecation over time, and certain engine features available on‑premises are either unavailable or limited in Azure, creating a compatibility boundary that affects lift‑and‑shift decisions.

What compatibility level should be retained to maintain existing query plans while still allowing adoption of newly supported features? How can the potential impact of a compatibility level change be evaluated before cutover without affecting production workloads? What are the operational risks of staying on an older compatibility level given the service’s deprecation schedule for those levels?