Sqlserver Merge マージ

CREATE TABLE City( 
    ID INTEGER PRIMARY KEY
  , CityName VARCHAR (100)
  , StateName VARCHAR (100)
); 

CREATE TABLE #CityTemp( 
    ID INTEGER PRIMARY KEY
  , CityName VARCHAR (100)
  , StateName VARCHAR (100)
);

Merge Into City
Using (
    Select
        ID
      , CityName
      , StateName
    From
        #CityTemp
    ) As X
On (    
        City.ID = X.ID
    )
When Matched Then
    Update Set
        CityName = X.CityName
      , StateName = X.StateName
When Not Matched Then
    Insert (
        CityName
      , StateName
    ) Values (
        X.CityName
      , X.StateName
      , GYMCOD
    )
;