可以使用  DENSE_RANK window function.
SELECT *
FROM (
	SELECT *,DENSE_RANK() OVER(PARTITION BY [季] ORDER BY [修改版次] DESC) rn
	FROM T 
    WHERE buy IS NOT NULL
) t1
WHERE rn = 1
SELECT 季,MAX(修改版次),BUY,MAX(price)
  FROM Table 1
  GROUP BY 季,BUY