使用窗口函数计算移动总和/平均值时的动态行范围（SQL Server）答案

【问题标题】：Dynamic row range when calculating moving sum/average using window functions (SQL Server)使用窗口函数计算移动总和/平均值时的动态行范围（SQL Server）
【发布时间】：2015-06-24 02:25:12
【问题描述】：

我目前正在编写一个示例脚本，它允许我计算前两行和当前行的总和。但是，我想将数字“2”作为变量。我尝试过声明一个变量，或者直接在查询中进行强制转换，但总是会弹出语法错误。有没有可能的解决方案？

DECLARE @myTable TABLE  (myValue INT)

INSERT INTO @myTable ( myValue ) VALUES  ( 5)
INSERT INTO @myTable ( myValue ) VALUES  ( 6)
INSERT INTO @myTable ( myValue ) VALUES  ( 7)
INSERT INTO @myTable ( myValue ) VALUES  ( 8)
INSERT INTO @myTable ( myValue ) VALUES  ( 9)
INSERT INTO @myTable ( myValue ) VALUES  ( 10)

SELECT 
    SUM(myValue) OVER (ORDER BY myValue 
                       ROWS BETWEEN 2 PRECEDING AND CURRENT ROW)
FROM @myTable

【问题讨论】：

你能不能建立一个动态的T-SQL 语句然后执行它？
是的，我可以尝试 - 目前这似乎是唯一的出路。但是想检查是否有任何其他“更清洁”的解决方案！非常感谢！

标签： sql sql-server tsql window-functions

【解决方案1】：

DECLARE @test VARCHAR = 1
DECLARE @sqlCommand VARCHAR(1000)
DECLARE @myTable TABLE  (myValue INT)

INSERT INTO @myTable ( myValue ) VALUES  ( 5)
INSERT INTO @myTable ( myValue ) VALUES  ( 6)
INSERT INTO @myTable ( myValue ) VALUES  ( 7)
INSERT INTO @myTable ( myValue ) VALUES  ( 8)
INSERT INTO @myTable ( myValue ) VALUES  ( 9)
INSERT INTO @myTable ( myValue ) VALUES  ( 10)

SET @sqlCommand = 'SELECT SUM(myValue) OVER (ORDER BY myValue ROWS BETWEEN ' + @test + ' PRECEDING AND CURRENT ROW)
                  FROM #temp'

EXEC (@sqlCommand)

【讨论】：

【解决方案2】：

您可以尝试这样的不使用动态 SQL 的方法。

DECLARE @myTable TABLE  (myValue INT)

INSERT INTO @myTable ( myValue ) VALUES  ( 5)
INSERT INTO @myTable ( myValue ) VALUES  ( 6)
INSERT INTO @myTable ( myValue ) VALUES  ( 7)
INSERT INTO @myTable ( myValue ) VALUES  ( 8)
INSERT INTO @myTable ( myValue ) VALUES  ( 9)
INSERT INTO @myTable ( myValue ) VALUES  ( 10)


DECLARE @prev_records INT = 2

;WITH CTE as 
(
SELECT ROW_NUMBER() OVER(ORDER BY myValue) rn,myValue FROM @myTable
)
SELECT (SELECT  SUM(myValue) FROM CTE t2 WHERE t2.rn BETWEEN (t1.rn  - @prev_records) AND t1.rn )
FROM CTE t1

SUM(myValue) OVER() 是最佳选择，但它不允许您使用变量传递前 N 行。

【讨论】：

【解决方案3】：

如果范围变量的可能离散度不是很高，可以使用简单的CASE语句在计算之间切换

DECLARE @myTable TABLE  (myValue INT)

-- let's say it could be between 1 and 10
DECLARE @range int = 3;

INSERT INTO @myTable ( myValue ) VALUES  ( 5)
INSERT INTO @myTable ( myValue ) VALUES  ( 6)
INSERT INTO @myTable ( myValue ) VALUES  ( 7)
INSERT INTO @myTable ( myValue ) VALUES  ( 8)
INSERT INTO @myTable ( myValue ) VALUES  ( 9)
INSERT INTO @myTable ( myValue ) VALUES  ( 10)

SELECT 
    CASE @range
        WHEN 1 THEN SUM(myValue) OVER (ORDER BY myValue ROWS BETWEEN 1 PRECEDING AND CURRENT ROW)
        WHEN 2 THEN SUM(myValue) OVER (ORDER BY myValue ROWS BETWEEN 2 PRECEDING AND CURRENT ROW)
        WHEN 3 THEN SUM(myValue) OVER (ORDER BY myValue ROWS BETWEEN 3 PRECEDING AND CURRENT ROW)
        WHEN 4 THEN SUM(myValue) OVER (ORDER BY myValue ROWS BETWEEN 4 PRECEDING AND CURRENT ROW)
        WHEN 5 THEN SUM(myValue) OVER (ORDER BY myValue ROWS BETWEEN 5 PRECEDING AND CURRENT ROW)
        WHEN 6 THEN SUM(myValue) OVER (ORDER BY myValue ROWS BETWEEN 6 PRECEDING AND CURRENT ROW)
        WHEN 7 THEN SUM(myValue) OVER (ORDER BY myValue ROWS BETWEEN 7 PRECEDING AND CURRENT ROW)
        WHEN 8 THEN SUM(myValue) OVER (ORDER BY myValue ROWS BETWEEN 8 PRECEDING AND CURRENT ROW)
        WHEN 9 THEN SUM(myValue) OVER (ORDER BY myValue ROWS BETWEEN 9 PRECEDING AND CURRENT ROW)
        WHEN 10 THEN SUM(myValue) OVER (ORDER BY myValue ROWS BETWEEN 10 PRECEDING AND CURRENT ROW)
    END
FROM @myTable

【讨论】：