sql，比较子查询中的聚合平均函数

Question

我的问题如下，ServiceTypeWithAvgPriceBelowAvgServicePrice 是一个提供平均价格低于平均服务价格的服务类型详细信息的视图。使用示例数据，以下查询应产生以下结果：

ServiceType                | ServiceTypeAvgPrice | ServiceAvgPrice
3rd drafting               |   280               |   522.7083
4th drafting               |   320               |   522.7083
client consultation        | 172.5               |   522.7083
design selection           |   300               |   522.7083
initial consultation       |     0               |   522.7083

样本数据

Description             Actual Price
initial consultation    $0
initial consultation    $0
design selection        $300
drafting                $1200
council approval        $600
client consultation     $360
develop design          $2070
client consultation     $180
client consultation     $180
client consultation     $135
initial consultation    $0
design selection        $300
drafting                $1200
council approval        $600
client consultation     $90
1st drafting            $1920
2nd drafting            $920
3rd drafting            $280
council approval        NULL
initial consultation    $0
initial consultation    $0
design selection        $300
drafting                $1500
council approval        $600
client consultation     $90
4th drafting            $320
initial consultation    $0

我试图检索低于实际价格总平均值的 5 个平均值，但我很难将每个独特描述的平均值与总价格进行比较。我正在尝试如下子查询，

select avg(actualPrice) as serviceytpeAvg 
from service 
having avg(actualprice) > (
                    select avg(actualprice) 
                    from service 
                    group by descrption)

但它被拒绝了，因为它不能为子查询返回一个以上的值。解决办法是什么？

Answer 1

您可以使用外部应用

SELECT  s.[Description] as ServiceType, 
        AVG(s.[Actual Price]) as ServiceTypeAvgPrice ,
        AvgPrice as ServiceAvgPrice
FROM [Service] s
OUTER APPLY (
    SELECT  AVG(s.[Actual Price]) as AvgPrice
    FROM [Service] s) p
GROUP BY s.[Description], AvgPrice
HAVING AVG(s.[Actual Price]) < AvgPrice

或者简单：

SELECT  s.[Description] as ServiceType, 
        AVG(s.[Actual Price]) as ServiceTypeAvgPrice ,
        (SELECT AVG([Actual Price]) FROM [Service]) as ServiceAvgPrice
FROM [Service] s
GROUP BY s.[Description]
HAVING AVG(s.[Actual Price]) < (SELECT AVG([Actual Price]) FROM [Service])

输出：

ServiceType             ServiceTypeAvgPrice ServiceAvgPrice
3rd drafting            280,00              505,5769
4th drafting            320,00              505,5769
client consultation     172,50              505,5769
design selection        300,00              505,5769
initial consultation    0,00                505,5769