🚧 MERGE (safe upserts)

🚧 Coming soon: MERGE basics, concurrency cautions, and safer alternatives.

-- Placeholder
MERGE dbo.Target AS t
USING (SELECT 1 AS Id, N'X' AS Name) s
ON t.Id = s.Id
WHEN MATCHED THEN UPDATE SET t.Name = s.Name
WHEN NOT MATCHED THEN INSERT (Id, Name) VALUES (s.Id, s.Name);