Merge - Only update if values have changed

Question

I am running a merge in SQL Server. In my update, I want to only update the row if the values have changed. There is a version row that increments on each update. Below is an example:

MERGE Employee as tgt USING  (SELECT Employee_History.Emp_ID , Employee_History.First_Name , Employee_History.Last_Name FROM Employee_History) as src (Emp_ID,First_Name,Last_Name) ON tgt.Emp_ID = src.Emp_ID WHEN MATCHED THEN      UPDATE SET     Emp_ID = src.Emp_ID,     ,[VERSION] = tgt.VERSION + 1      ,First_Name = src.First_Name     ,Last_Name = src.Last_Name WHEN NOT MATCHED BY target THEN      INSERT (Emp_ID,0,First_Name,Last_Name) VALUES      (src.Emp_ID,[VERSION],src.First_Name,src.Last_Name); 

Now, if I only wanted to update the row, and thus increment version, ONLY if the name has changed.

Answer 1

WHEN MATCHED can have AND . Also, no need to update EMP_ID .

...  WHEN MATCHED AND (trg.First_Name <> src.First_Name     OR trg.Last_Name <> src.Last_Name) THEN UPDATE    SET     [VERSION] = tgt.VERSION + 1      ,First_Name = src.First_Name     ,Last_Name = src.Last_Name  ... 

If Last_Name or First_Name are nullable, you need to take care of NULL values while comparing trg.Last_Name <> src.Last_Name , for instance ISNULL(trg.Last_Name,'') <> ISNULL(src.Last_Name,'')