Q7 Med

SELECT a.id, 
   b.age, 
   a.coins_needed, 
   a.power 
FROM wands a 
   JOIN wands_property b 
     ON a.code = b.code 
WHERE b.is_evil = 0 
    AND a.coins_needed = (SELECT Min(a1.coins_needed) 
    FROM wands a1 
        JOIN wands_property b1 
          ON a1.code = b1.code 
    WHERE b.age = b1.age 
        AND a.power = a1.power) 
ORDER BY a.power DESC, 
          b.age DESC;