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SQL Server Query Plan Forcing is a powerful feature that allows DBAs to fix a specific query plan for a query. This ensures consistent performance by preventing automatic changes to the query plan due to factors like statistics updates or SQL Server version upgrades. This feature, introduced in SQL Server 2016 and enhanced in SQL Server 2019, is especially useful for sensitive workloads where even minor fluctuations in query performance can have a significant impact.

To force a query plan in SQL Server 2019, you first need to identify the plan_id of the desired query plan. You can do this by querying the sys.query_store_plan system view. Once you have the plan_id, you can force the plan using the sp_query_store_force_plan stored procedure. For example:

-- Identify plan_id

SELECT plan_id FROM sys.query_store_plan WHERE query_id = 1234

-- Force the plan

EXEC sp_query_store_force_plan 1234, 5678

MySQL 8.0 does not directly support query plan forcing. However, it is possible to influence MySQL's query optimizer to choose a specific plan using hints. DB2 11.5, on the other hand, has a feature called Plan Management. This feature allows you to capture, compare, and control the use of query access plans, thereby achieving a similar outcome as SQL Server Query Plan Forcing.

Azure SQL, which is essentially SQL Server running on the Azure cloud platform, also supports query plan forcing. The process is identical to that on SQL Server: you identify the plan_id from the sys.query_store_plan system view and then execute the sp_query_store_force_plan stored procedure.

Azure Synapse, previously known as SQL Data Warehouse, is a fully managed cloud data warehouse for enterprises. It uses a different approach to query optimization and execution, and does not support the traditional query plan forcing. Instead, it relies on its sophisticated Massively Parallel Processing (MPP) architecture to optimize queries.

In conclusion, query plan forcing is a powerful tool for ensuring consistent query performance. Its availability and implementation vary between SQL Server, MySQL, DB2, and Azure SQL. Regardless of the specific technology in use, it is crucial to understand your database's query optimization and execution mechanisms to effectively manage and optimize query performance.