Question

ACCESS SQL 如何先计算总数再算平均数？我把SUM和AVG一起用的时候，显示在表达式中不能有聚合函数

SELECT CategoryRef, AVG(SUM(NumShares+NumFacebook)) AS AverageShares
FROM News
GROUP BY CategoryRef
ORDER BY AVG(NumShares) DESC;

Answer 1

avg就是把所有行的都加到一起，然后除以条数
所以你无须sum，这样就好

SELECT CategoryRef, AVG(NumShares+NumFacebook) AS AverageShares
FROM News
GROUP BY CategoryRef
ORDER BY AVG(NumShares) DESC;

Answer 2

select avg(AverageShares) AverageShares
from ( SELECT CategoryRef, SUM(NumShares+NumFacebook) AS AverageShares
FROM News
GROUP BY CategoryRef ) a
group by CategoryRef