mysql - 计算属性总和的 SQL 平均值

Question

我试图取某个类别值的平均值，其中行按子类别分组并计算总和。父表的主键是子表的分组属性。父表的分组属性既不是主键，也不是子表中的。

简单表示:

select Category, avg(CalculatedSum)
from ParentTable pt
inner join (
    select Subcategory, sum(Quantity * Price) as 'CalculatedSum'
    from ChildTable
    group by Subcategory
    ) ct
on pt.ID = ct.Subcategory
group by Category

实际的SQL如下:

select c.CU_AGE_RANGE, count(*) as '# of Customers', avg(SumSales) as 'Avg of SumSales', max([Max of SumSales]) as 'Max of SumSales', min([Min of SumSales]) as 'Min of SumSales'
from Customers c
inner join (
    select CUSTOMER_ID, sum(QTY_SOLD * SALES) as SumSales, max(QTY_SOLD*SALES) as 'Max of SumSales', min(QTY_SOLD*SALES) as 'Min of SumSales'
    from Sales
    where (SALES > 0) and (QTY_SOLD > 0) and (COST > 0)
    Group by CUSTOMER_ID
    ) s
on c.CUSTOMER_ID = s.CUSTOMER_ID
group by c.CU_AGE_RANGE

我尝试将 group by 子句更改为类别 (CU_AGE_RANGE) 和子类别 (CUSTOMER_ID) 的各种顺序，但始终遇到相同的错误。

错误在于该表将始终向我显示总和的总和(我相信)。我假设这是错误，因为子表中的典型平均值为 250 到 1000，并且 Avg(Sum()) 返回的值大致为每个类别的行数乘以预期的 Sum()。

由于声誉较低，我无法发布照片，因此请参阅以下逗号分隔结果表:

CU_AGE_RANGE,#_of_Customers,Avg_of_SumSales,Max_of_SumSales,Min_of_SumSales
NULL,125,4261665.306,433460737.7,0.0017
20-29     ,1192,1154040.907,1374037708,0.00025
30-39     ,1902,25429.52329,29426212.64,0.00015
40-49     ,2118,2418.829874,2066725,0.0001
50-59     ,2204,114625.4111,248240261.3,0.00015
60+       ,2135,160156.4341,334617675,0.0005
patrickbig,1,65.5737,12,0.06
Under 19  ,484,1431.262112,92160,0.0001

我试图弄清楚为什么 AVG(SUM()) 返回的内容似乎是 SUM(SUM())。我当前的预感是，由于 SUM() 是计算条目，因此计算值是根据父表中的分组重新计算的。所以这将是:

期望:

x * y for each row in Child Table
sum(x*y) for each Subcategory
Avg(sum(x/y)) for each Category of Subcategory

QTY_SOLD * SALE for each row in Sales
sum(QTY_SOLD*SALE) for each CUSTOMER_ID
avg(sum(QTY_SOLD*SALE) for each CU_AGE_RANGE group of CUSTOMER_IDs

实际:

x * y for each row in Child Table                  
sum(x * y) for each Subcategory
avg(sum(x * y) for each Category

avg(sum(QTY_SOLD*SALE) for each CU_AGE_RANGE

等于:

sum(QTY_SOLD*SALE) for each CU_AGE_RANGE

如何从当前(类别总和)到所需(按类别的子类别总和的平均值)？

Answer 1

您的客户计数有误。您计算的是销售额，而不是客户数量。更改为 count( DISTINCT c.CUSTOMER_ID ) 应该可以解决问题。

select c.CU_AGE_RANGE, count( DISTINCT c.CUSTOMER_ID ) as '# of Customers', avg(SumSales) as 'Avg of SumSales', max([Max of SumSales]) as 'Max of SumSales', min([Min of SumSales]) as 'Min of SumSales'
from Customers c
inner join (
    select CUSTOMER_ID, sum(QTY_SOLD * SALES) as SumSales, max(QTY_SOLD*SALES) as 'Max of SumSales', min(QTY_SOLD*SALES) as 'Min of SumSales'
    from Sales
    where (SALES > 0) and (QTY_SOLD > 0) and (COST > 0)
    Group by CUSTOMER_ID
    ) s
on c.CUSTOMER_ID = s.CUSTOMER_ID
group by c.CU_AGE_RANGE