使用递归CTE计算预测平均值

Question

我试图在这里回答一个问题,我需要根据之前的3个月来计算销售预测,这可能是实际的或预测的.

Month   Actuals Forecast  
1       10    
2       15    
3       17    
4                14.00 
5                15.33  
6                15.44 
7                14.93

Month 4 = (10+15+17)/3 
Month 5 = (15+17+14)/3 
Month 6 = (17+14+15.33)/3
Month 7 = (14+15.33+15.44)/3

我一直在尝试使用递归CTE来做到这一点:

;WITH cte([month],forecast) AS (
    SELECT 1,CAST(10 AS DECIMAL(28,2))
    UNION ALL
    SELECT 2,CAST(15 AS DECIMAL(28,2))
    UNION ALL 
    SELECT 3,CAST(17 AS DECIMAL(28,2))
    UNION ALL
    SELECT
        [month]=[month]+1,
        forecast=CAST(AVG(forecast) OVER (ORDER BY [month] ROWS BETWEEN 3 PRECEDING AND 1 PRECEDING) AS DECIMAL(28,2))
    FROM
        cte
    WHERE
        [month]<=12
)
SELECT * FROM cte WHERE month<=12;

小提琴:http://sqlfiddle.com/#!6/9ac4a/3

但它没有按预期工作,因为它返回以下结果:

| month | forecast |
|-------|----------|
|     1 |       10 |
|     2 |       15 |
|     3 |       17 |
|     4 |   (null) |
|     5 |   (null) |
|     6 |   (null) |
|     7 |   (null) |
|     8 |   (null) |
|     9 |   (null) |
|    10 |   (null) |
|    11 |   (null) |
|    12 |   (null) |
|     3 |   (null) |
|     4 |   (null) |
|     5 |   (null) |
|     6 |   (null) |
|     7 |   (null) |
|     8 |   (null) |
|     9 |   (null) |
|    10 |   (null) |
|    11 |   (null) |
|    12 |   (null) |
|     2 |   (null) |
|     3 |   (null) |
|     4 |   (null) |
|     5 |   (null) |
|     6 |   (null) |
|     7 |   (null) |
|     8 |   (null) |
|     9 |   (null) |
|    10 |   (null) |
|    11 |   (null) |
|    12 |   (null) |

预期产量:

| month | forecast |
|-------|----------|
|     1 |       10 |
|     2 |       15 |
|     3 |       17 |
|     4 |    14.00 |
|     5 |    15.33 |
|     6 |    15.44 |
|     7 |    14.93 |
|     8 |    15.23 |
|     9 |    15.20 |
|    10 |    15.12 |
|    11 |    15.18 |
|    12 |    15.17 |

有人能告诉我这个查询有什么问题吗？

Answer 1

我建议这样的事情:

WITH T AS
(
    SELECT 1 AS [month], CAST(10 AS DECIMAL(28,2)) AS [forecast], CAST(-5 AS DECIMAL(28,2)) AS three_months_ago_forecast, CAST(9 AS decimal(28,2)) AS two_months_ago_forecast, CAST(26 AS decimal(28,2)) as one_month_ago_forecast
    UNION ALL
    SELECT 2,CAST(15 AS DECIMAL(28,2)), CAST(9 AS decimal(28,2)), CAST(26 AS decimal(28,2)), CAST(10 AS DECIMAL(28,2))
    UNION ALL 
    SELECT 3,CAST(17 AS DECIMAL(28,2)), CAST(26 AS decimal(28,2)), CAST(10 AS DECIMAL(28,2)), CAST(15 AS DECIMAL(28,2))
),
LT AS -- LastForecast
(
    SELECT *
    FROM T
    WHERE [month] = 3
),
FF AS -- Future Forecast
(
    SELECT *
    FROM LT

    UNION ALL

    SELECT 
        FF.[month] + 1 AS [month], 
        CAST( (FF.forecast * 4 - FF.three_months_ago_forecast) / 3 AS decimal(28,2)) AS forecast,
        FF.two_months_ago_forecast as three_months_ago_forecast,
        FF.one_month_ago_forecast as two_months_ago_forecast,
        FF.forecast as one_month_ago_forecast
    FROM FF
    WHERE
        FF.[month] < 12

)
SELECT * FROM T
WHERE [month] < 3
UNION ALL
SELECT * FROM FF

输出:

+-------+----------+---------------------------+-------------------------+------------------------+
| month | forecast | three_months_ago_forecast | two_months_ago_forecast | one_month_ago_forecast |
+-------+----------+---------------------------+-------------------------+------------------------+
|     1 | 10.00    | -5.00                     | 9.00                    | 26.00                  |
|     2 | 15.00    | 9.00                      | 26.00                   | 10.00                  |
|     3 | 17.00    | 26.00                     | 10.00                   | 15.00                  |
|     4 | 14.00    | 10.00                     | 15.00                   | 17.00                  |
|     5 | 15.33    | 15.00                     | 17.00                   | 14.00                  |
|     6 | 15.44    | 17.00                     | 14.00                   | 15.33                  |
|     7 | 14.92    | 14.00                     | 15.33                   | 15.44                  |
|     8 | 15.23    | 15.33                     | 15.44                   | 14.92                  |
|     9 | 15.20    | 15.44                     | 14.92                   | 15.23                  |
|    10 | 15.12    | 14.92                     | 15.23                   | 15.20                  |
|    11 | 15.19    | 15.23                     | 15.20                   | 15.12                  |
|    12 | 15.18    | 15.20                     | 15.12                   | 15.19                  |
+-------+----------+---------------------------+-------------------------+------------------------+