关于sQL的问题，轻而易举拿分来！
帮我看看 为什么sum(TotalMil.TotalMil)统计了两次
实际TotalMil表里只有一个记录，而GravyBoatInfo有两条记录 由于这种原因造成的 该怎么改动

SELECT GravyBoatInfo.CarBrandCode,sum(Amount) AS 总耗油量（升）, sum(TotalMil.TotalMil) as 总公里数（Km）,
sum(Amount)/sum(TotalMil.TotalMil)*100 AS 百公里油耗
FROM GravyBoatInfo, TotalMil
WHERE GravyBoatInfo.CarBrandCode=TotalMil.CarBrandCode
GROUP BY GravyBoatInfo.CarBrandCode,TotalMil.CarBrandCode



[解决办法]
SELECT GravyBoatInfo.CarBrandCode,sum(Amount) AS 总耗油量（升）, sum(TotalMil.TotalMil) as 总公里数（Km）,
sum(Amount)/sum(TotalMil.TotalMil)*100 AS 百公里油耗
FROM GravyBoatInfo, TotalMil
WHERE GravyBoatInfo.CarBrandCode=TotalMil.CarBrandCode
GROUP BY GravyBoatInfo.CarBrandCode