USE Northwind;

--INTERSECT   
   SELECT Country, Region, City
     FROM Customers
INTERSECT
   SELECT Country, Region, City
     FROM Employees;
     
     
--UNION ALL
SELECT D.Country, D.Region, D.City
  FROM (SELECT DISTINCT Country, Region, City 
          FROM Customers
         UNION ALL
        SELECT DISTINCT Country, Region, City
          FROM Employees) AS D
 GROUP BY D.Country, D.Region, D.City
HAVING COUNT(*) = 2;
     
--EXISTS
SELECT DISTINCT Country, Region, City
  FROM Customers AS C
 WHERE EXISTS
       (SELECT *
          FROM Employees AS E
         WHERE COALESCE(C.Country, '1') = COALESCE(E.Country, '1')
           AND COALESCE(C.Region, '1') = COALESCE(E.Region, '1')
           AND COALESCE(C.City, '1') = COALESCE(E.City, '1'));
           
--IN
SELECT DISTINCT Country, Region, City
  FROM Customers AS C
 WHERE COALESCE(C.Country, '1') IN 
       (SELECT COALESCE(E.Country, '1')
          FROM Employees AS E
         WHERE COALESCE(C.Region, '1') = COALESCE(E.Region, '1')
           AND COALESCE(C.City, '1') = COALESCE(E.City, '1'));
    
    
--JOIN
SELECT DISTINCT C.Country, C.Region, C.City
  FROM Customers AS C
  JOIN Employees AS E
    ON COALESCE(C.Country, '1') = COALESCE(E.Country, '1')
   AND COALESCE(C.Region, '1') = COALESCE(E.Region, '1')
   AND COALESCE(C.City, '1') = COALESCE(E.City, '1');


--EXCEPT
SELECT Country, Region, City
  FROM Customers
EXCEPT (SELECT Country, Region, City
          FROM Customers
        EXCEPT
        SELECT Country, Region, City
          FROM Employees);