SQL Merge

When writing an SQL Merge Statement, I wanted to avoid updating rows that hadn't changed. 

The trick is to use EXISTS and EXCEPT 

The page at http://www.made2mentor.com/2013/05/writing-t-sql-merge-statements-the-right-way/ explains this well

There's also a reference to Paul White's page https://www.sql.kiwi/

MERGE  #Customer_New AS Target
 USING #Customer_Orig AS Source
    ON Target.CustomerNum = Source.CustomerNum
WHEN MATCHED AND EXISTS
                    (SELECT Source.CustomerName, Source.Planet
                     EXCEPT
                     SELECT Target.CustomerName, Target.Planet)
THEN
   UPDATE SET
      Target.CustomerName = Source.CustomerName
     ,Target.Planet = Source.Planet
WHEN NOT MATCHED BY TARGET
THEN
   INSERT (CustomerNum, CustomerName, Planet)
   VALUES (CustomerNum, Source.CustomerName, Source.Planet)
WHEN NOT MATCHED BY SOURCE THEN DELETE;