Erik Darling defends the honor of the MERGE statement:
In this video, I delve into the often maligned `MERGE` statement in SQL Server, defending it against its critics and highlighting its unique benefits. You might be surprised to learn that `MERGE` can actually help catch non-deterministic updates—something a standard `UPDATE` query won’t do. By demonstrating how `MERGE` issues a warning when you attempt a non-deterministic update, I aim to show why this statement deserves more respect in your database toolkit. The video also covers practical solutions for making these updates deterministic using window functions like `ROW_NUMBER()`, ensuring that the data integrity and consistency you expect from SQL Server are maintained. Whether you’re looking to improve query reliability or just want to understand a lesser-used feature better, there’s something here for everyone who deals with complex data operations in SQL Server.
Alongside this, I recommend a post from Hugo Kornelis from a few years ago, looking into pretty much every problem people reported with MERGE and checking to see if it was still and issue and, if so, under what circumstances.