Sql server 如何计算每个月的数量，然后在同一select语句中取其平均值

在如下情况下，如何计算每月总平均数？：

我们有9个claimID。因此，平均航程为9/6个月=1.5个月

DECLARE @TestTable TABLE (claimid int, DateClosed datetime)

INSERT INTO @TestTable  
VALUES (111, '01-01-2018'), (222, '01-03-2018'), (333, '01-12-2018'),
       (444, '07-03-2018'), (555, '08-15-2018'), (666, '09-13-2018'),
       (777, '04-03-2019'), (888, '05-01-2019'), (999, '07-01-2018'),
       (1000, NULL), (1100, NULL), (1200, NULL)

SELECT 
    ClaimID,
    CAST(DateClosed AS DATE) AS DateClosed,
    COUNT(ClaimID) CountClaimID,
    COUNT(claimid) OVER (PARTITION BY MONT(DateClosed), YEAR(DateClosed)) AS CountPerMonth
FROM 
    @TestTable
GROUP BY 
    ClaimID, DateClosed

---

也许是这样的

示例

SELECT ClaimID
       ,cast(DateClosed AS date) AS DateClosed
       ,count(ClaimID) CountClaimID
       ,count(claimid) OVER ( PARTITION BY Month(DateClosed), year(DateClosed)) AS CountPerMonth
       ,case when DateClosed is null then 0 else count(DateClosed) over () / (select 0.0+count(distinct left(cast(DateClosed as date),7)) from @TestTable) end AS TotalAverage
FROM   @TestTable
GROUP  BY ClaimID,DateClosed

返回

---

1.5是什么的平均数？每年每月的索赔平均数。所以我们总共有9个claimId/6个不同的月=1.5John，太神奇了！在我真正的查询中，我只有

NULL

，有时是

DateClosed

。是否有任何方法可以对只有

DateClosed

的

count（ClaimID）

？@Oleg进行空值更新。希望这有帮助。哦！你改为计算了

DateClosed

！因为我尝试了案例陈述，但我仍然计算了

ClaimID

。非常感谢。