(PaaS) Azure SQL DB is for one standalone database and is mostly for transactional systems like web sites (1)
https://www.brentozar.com/archive/2019/02/how-fast-can-a-21468-mo-azure-sql-db-load-data/(1) https://www.brentozar.com/archive/2021/04/azure-sql-db-frequently-asked-questions/https://www.brentozar.com/archive/2017/06/builder-day-point-time-restore-azure-sql-db/(PaaS) Azure SQL Managed Instance is designed for customers looking to migrate a large number of apps from an on-premises or IaaS, self-built, or ISV provided environment to a fully managed PaaS cloud environment (2)
(2) https://docs.microsoft.com/en-us/azure/azure-sql/managed-instance/sql-managed-instance-paas-overviewSynapse Analytics is for data warehouses (1)
(1) https://www.brentozar.com/archive/2021/04/azure-sql-db-frequently-asked-questions/https://azure.microsoft.com/en-us/services/synapse-analytics/Small-footprint, edge-optimized SQL database engine with built-in AI (3)
(3) https://azure.microsoft.com/en-us/services/sql-edge/