Константин Цветков

SELECT t.id, t.country, t.salary 
  FROM t
    INNER JOIN 
      ( SELECT country, max(salary) AS max_salary FROM t GROUP BY country ) tm
        ON t.country = tm.country AND t.salary = tm.max_salary

SELECT t.id, dt, curr,  rate 
  FROM t 
   INNER JOIN
      ( SELECT id, COUNT(*)
        FROM t
        GROUP BY id
        HAVING COUNT(*) > 1 ) t_count ON t.id = t_count.id