Tsql 表子集的T-SQL平均

我在SQL Server 2005中有一个针对单个位置的每日天气数据表，其中包括以下列：

LogDate                 DATETIME  
HighTemp                INT  
Temp6MonthHighAverage   INT  

LogDate和HighTemp有数据。顾名思义，HighTemp6MonthAverage将填充以LogDate结束的6个月内的平均高温

对于跨越数十年的数据，对低温、湿度和其他几个项目也有类似的要求

---

我发现自己在兜圈子。我可以使用set操作为UPDATE语句中的每一行导出此平均值，还是需要使用游标实现解决方案？如果有任何建议，我将不胜感激。

看看这样的建议

DECLARE @Table TABLE(
    LogDate DATETIME,
    HighTemp INT,
    Temp6MonthHighAverage INT
)

INSERT INTO @Table SELECT '01 Jan 2000', 15, NULL
INSERT INTO @Table SELECT '01 May 2000', 14, NULL
INSERT INTO @Table SELECT '01 Jun 2000', 13, NULL
INSERT INTO @Table SELECT '01 Jul 2000', 12, NULL
INSERT INTO @Table SELECT '01 Dec 2000', 17, NULL

SELECT  *
FROM    @Table

;WITH DistinctDates AS (
        SELECT  DATEADD(month,-6,LogDate) StartDate,
                LogDate EndDate,
                HighTemp
        FROM    @Table
)
, Aggregates AS (
        SELECT  dd.EndDate LogDate,
                dd.HighTemp,
                MAX(t.HighTemp) Temp6MonthHighAverage
        FROM    DistinctDates dd LEFT JOIN
                @Table t    ON  t.LogDate BETWEEN dd.StartDate AND dd.EndDate
        GROUP BY    dd.EndDate,
                    dd.HighTemp
)
UPDATE  @Table
SET     Temp6MonthHighAverage = a.Temp6MonthHighAverage
FROM    @Table t INNER JOIN
        Aggregates a    ON  t.LogDate = a.LogDate

SELECT  *
FROM    @Table

---

看看这样的东西

DECLARE @Table TABLE(
    LogDate DATETIME,
    HighTemp INT,
    Temp6MonthHighAverage INT
)

INSERT INTO @Table SELECT '01 Jan 2000', 15, NULL
INSERT INTO @Table SELECT '01 May 2000', 14, NULL
INSERT INTO @Table SELECT '01 Jun 2000', 13, NULL
INSERT INTO @Table SELECT '01 Jul 2000', 12, NULL
INSERT INTO @Table SELECT '01 Dec 2000', 17, NULL

SELECT  *
FROM    @Table

;WITH DistinctDates AS (
        SELECT  DATEADD(month,-6,LogDate) StartDate,
                LogDate EndDate,
                HighTemp
        FROM    @Table
)
, Aggregates AS (
        SELECT  dd.EndDate LogDate,
                dd.HighTemp,
                MAX(t.HighTemp) Temp6MonthHighAverage
        FROM    DistinctDates dd LEFT JOIN
                @Table t    ON  t.LogDate BETWEEN dd.StartDate AND dd.EndDate
        GROUP BY    dd.EndDate,
                    dd.HighTemp
)
UPDATE  @Table
SET     Temp6MonthHighAverage = a.Temp6MonthHighAverage
FROM    @Table t INNER JOIN
        Aggregates a    ON  t.LogDate = a.LogDate

SELECT  *
FROM    @Table

---

您当然可以通过简单的更新来做到这一点：

UPDATE table SET Temp6MonthHighAverage = 
  (SELECT AVG(HighTemp) FROM table t2 WHERE
     t2.LogDate <= table.LogDate
     AND t2.LogDate > DATEADD(m, -6, table.LogDate)
  )

---

由于过去不会改变，为了避免不断地重新计算，只需添加一个Temp6MonthHighAverage在结尾处为空的值，并且可以根据需要运行相同的更新，以在添加新日期时填补空白。

您当然可以通过简单的更新来完成此操作：

UPDATE table SET Temp6MonthHighAverage = 
  (SELECT AVG(HighTemp) FROM table t2 WHERE
     t2.LogDate <= table.LogDate
     AND t2.LogDate > DATEADD(m, -6, table.LogDate)
  )

-- select 
select HighTemp, LogDate,(select AVG(HighTemp) 
                          from tbl where 
                          DATEDIFF(MONTH, LogDate, t1.LogDate) between 0 and 6)
from tbl t1

-- update
update t1 set Temp6MonthHighAverage = (select AVG(HighTemp) 
                          from tbl where 
                          DATEDIFF(MONTH, LogDate, t1.LogDate) between 0 and 6)
from tbl t1

---

由于过去不会改变，为了避免不断地重新计算，只需添加一个Temp6MonthHighAverage在结尾处为空，并且可以根据需要运行相同的更新，以在添加新日期时填补空白。

您可以使用UPDATE语句来完成此操作，但我怀疑使用游标可能更有效，因为SQL Server可能无法实现滚动平均。请选择SQL Server的哪个版本？您可以使用UPDATE语句来实现，但我怀疑使用游标可能更有效，因为SQL Server可能无法实现滚动平均。请选择哪个版本的SQL Server？

-- select 
select HighTemp, LogDate,(select AVG(HighTemp) 
                          from tbl where 
                          DATEDIFF(MONTH, LogDate, t1.LogDate) between 0 and 6)
from tbl t1

-- update
update t1 set Temp6MonthHighAverage = (select AVG(HighTemp) 
                          from tbl where 
                          DATEDIFF(MONTH, LogDate, t1.LogDate) between 0 and 6)
from tbl t1