Question

我有一个非常简单的表：

Date, kWh

它有大约4年的数据。

如何生成如下结果集：

Year, Result
2010, 123211
2011, 123213
2012, 123211
2013, xxxxxx

其中xxxx是当年的预测。

预测将结合到目前为止2013年的日期总和，加上平均每千瓦时乘以2013年的剩余天数。

Answer 1

这将使用闰年正确计算预计使用量。如您所见，闰年计算比其他计算更具逻辑性。由于随着年份的进展投影越来越近，整年过去了，“预计”显示了实际使用情况。

SELECT DATEPART(YEAR, [Date]) year, SUM(kWh) * 
  (365 + ISDATE(CAST(DATEPART(YEAR, [DATE]) AS char(4)) + '0229')) / 
  COUNT(kWh) Projected
FROM readings
GROUP BY DATEPART(YEAR, [Date])

A simple SQLfiddle to test with

要使平均计数超过多年，需要稍微修改一下查询;

WITH average AS (SELECT AVG(kWh) kWh FROM readings)
SELECT DATEPART(YEAR, a.[Date]) year, SUM(a.kWh) + AVG(b.kWh) *
  ((365 + ISDATE(CAST(DATEPART(YEAR, a.[DATE]) AS char(4)) + '0229')) -
  COUNT(a.kWh)) Projected
FROM readings a, average b
GROUP BY DATEPART(YEAR, a.[Date])

这使用cte来计算稍后在查询中使用它的平均值。

Another SQLfiddle

Answer 2

假设每年都有365天，当然不是真的......

select Datepart(YEAR,[Date]) as [Year],
           case when Datepart(YEAR,[Date]) = Datepart(YEAR, getdate()) 
        then  365*Avg(Kwh)
        else  SUM(Kwh) end as TotalKwh
    from table_1
    group by Datepart(YEAR,[Date])

Answer 3

Yous应该进行两次查询。第一个是YEAR的简单组，第二个是关于去年，剩余天数，平均kWh的一行信息查询。然后juts LEFT JOIN这些表格，你会得到你想要的。

SQLFiddle demo

with t1 as
(
select 
       DATEPART(YEAR,[Date]) as Year,
       sum(kWh) SumKWH
from t
group by 
DATEPART(YEAR,[Date])
),
t2 as
(
select max(DATEPART(YEAR,[Date])) as MaxYear,
       AVG(kWH) as AverageKWH,
       DATEDIFF(DAY,max([Date]),
       CAST( CAST(max(DATEPART(YEAR,[Date])) as varchar(4))+'-12-31' as datetime)
                ) DaysLeft

from t
  )
select t1.YEAR, 
t1.SumKWH+ISNULL(AVERAGEKWH*DAYSLEFT,0)
from t1 
left join t2 on (t1.Year=t2.MaxYear)
order by t1.YEAR;

T-SQL选择每年的总和，并预测明年

3 个答案:

SQLFiddle demo