使用MAX（）和VALUES（）优化SQL语句

Question

在以下情况下，目标是返回股票的最高评级：

SELECT DISTINCT sd.ShareId
  , CASE 
      WHEN sd.GV01 IS NOT NULL OR sd.GV02 IS NOT NULL OR sd.GV03 IS NOT NULL THEN (
         SELECT MAX(val)
         FROM (VALUES (rmatMG.RankingId), (rmatSG.RankingId), (rmatFG.RankingId)) AS value(val)
         WHERE val IS NOT NULL
    ) 
  END AS minRating
  , sd.TradeValue
FROM dbo.MasterData sd
LEFT JOIN dbo.CfgRatingMatching rmMG ON sd.GV01 = rmMG.RatingIdOne 
LEFT JOIN dbo.CfgRatingmatrix rmatMG ON rmMG.RatingIdCollMatrix = rmatMG.RankingId
LEFT JOIN dbo.CfgRatingMatching rmSG ON sd.GV02 = rmSG.RatingIdTwo 
LEFT JOIN dbo.CfgRatingmatrix rmatSG ON rmSG.RatingIdCollMatrix = rmatSG.RankingId
LEFT JOIN dbo.CfgRatingMatching rmFG ON sd.GV03 = rmFG.RatingIdThree 
LEFT JOIN dbo.CfgRatingmatrix rmatFG ON rmFG.RatingIdCollMatrix = rmatFG.RankingId

有人知道如何优化代码吗？我有很多数据，返回列表几乎要花一分钟多的时间。需要太长时间。