包含SQL AVG，但在选择列表中获取Column无效，因为它不包含在聚合函数或GROUP BY子句中

Question

我对为什么会收到此错误感到非常困惑：

“列'City.CityID'在选择列表中无效，因为它既不包含在聚合函数中也不在GROUP BY子句中。”

我有两个表：一个名为City的城市信息，例如ID，名称等， 另一个表包含CityID和等级（可以有很多行具有相同的CityID和等级）。

我有一个城市group依据，我只是在RateCity表中获得平均评分。 那为什么会失败呢？

select City.CityID, City.CityName, City.CityStateOrProvince, 
City.CityCountry, City.CityImageUri, AVG(RateCity.Rating) as AverageRating
from City
right join RateCity
on City.CityID = RateCity.CityID
group by City.CityID, RateCity.CityID

Answer 1

您需要按所有非聚合分组。

select City.CityID
      ,City.CityName
      ,City.CityStateOrProvince
      ,City.CityCountry
      ,City.CityImageUri
      ,AVG(RateCity.Rating) as AverageRating
from City 
right join RateCity on City.CityID = RateCity.CityID
 Group by 
       City.CityID
      ,City.CityName
      ,City.CityStateOrProvince
      ,City.CityCountry
      ,City.CityImageUri

另一种选择是

select City.CityID
      ,City.CityName
      ,CityStateOrProvince = max(City.CityStateOrProvince)
      ,CityCountry         = max(City.CityCountry)
      ,CityImageUri        = max(City.CityImageUri)
      ,AverageRating       = AVG(RateCity.Rating) 
from City 
right join RateCity on City.CityID = RateCity.CityID
 Group by 
       City.CityID
      ,City.CityName

Answer 2

您只能在select子句中包含那些包含在group by子句中的列。 仅当对它们应用聚合函数时，才能选择任何其他列。 对于Ex-（正确的一个）

SELECT a,b,sum(c)
From d
GROUP BY a,b;

（错了）

SELECT a,b,sum(c)
FROM d
GROUP BY a;

Answer 3

您必须在组中包括所有不在聚集中的列

SELECT City.CityID, 
       City.CityName, 
       City.CityStateOrProvince, 
       City.CityCountry, 
       City.CityImageUri, 
       AVG(RateCity.Rating) as AverageRating
FROM City
RIGHT JOIN RateCity on City.CityID = RateCity.CityID
GROUP BY City.CityID, City.CityName, City.CityStateOrProvince, 
City.CityCountry, City.CityImageUri