用结果集系列中的最新非 NULL 值替换 NULL 值(SQL Server 2008 R2) [英] replace NULL values with latest non-NULL value in resultset series (SQL Server 2008 R2)

问题描述

对于 SQL Server 2008 R2

for SQL Server 2008 R2

我有一个看起来像这样的结果集(注意 [price] 是数字，下面的 NULL 表示NULL值，结果集按product_id和timestamp排序)

I have a resultset that looks like this (note [price] is numeric, NULL below represents a NULL value, the result set is ordered by product_id and timestamp)

product timestamp          price 
------- ----------------   -----
   5678 2008-01-01 12:00   12.34
   5678 2008-01-01 12:01    NULL
   5678 2008-01-01 12:02    NULL
   5678 2008-01-01 12:03   23.45
   5678 2008-01-01 12:04    NULL

我想将其转换为一个结果集，该结果集(本质上)从最新的前一行复制一个非空值，以生成如下所示的结果集:

I want to transform that to a result set that (essentially) copies a non-null value from the latest preceding row, to produce a resultset that looks like this:

product timestamp          price  
------- ----------------   -----
   5678 2008-01-01 12:00   12.34
   5678 2008-01-01 12:01   12.34
   5678 2008-01-01 12:02   12.34
   5678 2008-01-01 12:03   23.45
   5678 2008-01-01 12:04   23.45

我没有找到任何允许我执行此操作的聚合/窗口函数(同样，这仅适用于 SQL Server 2008 R2.)

I don't find any aggregate/windowing function that will allow me to do this (again this ONLY needed for SQL Server 2008 R2.)

我希望找到一个分析聚合函数来为我做这件事，比如......

I was hoping to find an analytic aggregate function that do this for me, something like...

LAST_VALUE(price) OVER (PARTITION BY product_id ORDER BY timestamp)

但我似乎没有找到任何方法在窗口中执行累积最新非空值"(将窗口绑定到前面的行，而不是整个分区)

But I don't seem to find any way to do a "cumulative latest non-null value" in the window (to bound the window to the preceding rows, rather than the entire partition)

除了创建一个表值的用户定义函数之外，是否有任何内置函数可以完成此操作?

Aside from creating a table-valued user defined function, is there any builtin that would accomplish this?

更新:

显然，此功能在Denali"CTP 中可用，但在 SQL Server 2008 R2 中不可用.

Apparently, this functionality is available in the 'Denali' CTP, but not in SQL Server 2008 R2.

LAST_VALUE http://msdn.microsoft.com/en-us/library/hh231517%28v=SQL.110%29.aspx

我只是希望它在 SQL Server 2008 中可用.它在 Oracle 中可用(至少从 10gR2 开始)，我可以在 MySQL 5.1 中使用局部变量执行类似的操作.

I just expected it to be available in SQL Server 2008. It's available in Oracle (since 10gR2 at least), and I can do something similar in MySQL 5.1, using a local variable.

http://download.oracle.com/docs/cd/E14072_01/server.112/e10592/functions083.htm

推荐答案

您可以尝试以下方法:

* 更新**

-- Test Data
DECLARE @YourTable TABLE(Product INT, Timestamp DATETIME, Price NUMERIC(16,4))

INSERT INTO @YourTable
SELECT 5678, '20080101 12:00:00', 12.34
UNION ALL
SELECT 5678, '20080101 12:01:00', NULL
UNION ALL
SELECT 5678, '20080101 12:02:00', NULL
UNION ALL
SELECT 5678, '20080101 12:03:00', 23.45
UNION ALL
SELECT 5678, '20080101 12:04:00', NULL

;WITH CTE AS
(
    SELECT *
    FROM @YourTable
)

-- Query
SELECT A.Product, A.Timestamp, ISNULL(A.Price,B.Price) Price
FROM CTE A
OUTER APPLY (   SELECT TOP 1 *
                FROM CTE 
                WHERE Product = A.Product AND Timestamp < A.Timestamp
                AND Price IS NOT NULL
                ORDER BY Product, Timestamp DESC) B

--Results
Product Timestamp   Price
5678    2008-01-01 12:00:00.000 12.3400
5678    2008-01-01 12:01:00.000 12.3400
5678    2008-01-01 12:02:00.000 12.3400
5678    2008-01-01 12:03:00.000 23.4500
5678    2008-01-01 12:04:00.000 23.4500

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