Unindo uma tabela consigo mesma vs usando Group By MySQL

SELECT e1.*
FROM employee e1
JOIN employee e2
  ON e1.employee_id <> e2.employee_id  
 AND e1.column2 = e2.column2 
 AND e1.X <> e2.X
 AND e1.Y <> e2.Y

AND (e1.X <> e2.X OR e1.Y <> e2.Y)