问题
for SQL Server 2008 R2
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
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
I don't find any aggregate/windowing function that will allow me to do this (again this ONLY needed for SQL Server 2008 R2.)
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)
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)
Aside from creating a table-valued user defined function, is there any builtin that would accomplish this?
UPDATE:
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
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
回答1:
You can try the following:
* Updated **
-- 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
回答2:
Try this:
;WITH SortedData AS
(
SELECT
ProductID, TimeStamp, Price,
ROW_NUMBER() OVER(PARTITION BY ProductID ORDER BY TimeStamp DESC) AS 'RowNum'
FROM dbo.YourTable
)
UPDATE SortedData
SET Price = (SELECT TOP 1 Price
FROM SortedData sd2
WHERE sd2.RowNum > SortedData.RowNum
AND sd2.Price IS NOT NULL)
WHERE
SortedData.Price IS NULL
Basically, the CTE creates a list sorted by timestamp (descending) - the newest first. Whenever a NULL is found, the next row that contains a NOT NULL price will be found and that value is used to update the row with the NULL price.
回答3:
I have a table containing the following data. I want to update all nulls in salary columns with previous value without taking null value.
Table:
id name salary
1 A 4000
2 B
3 C
4 C
5 D 2000
6 E
7 E
8 F 1000
9 G 2000
10 G 3000
11 G 5000
12 G
here is the query that works for me.
select a.*,first_value(a.salary)over(partition by a.value order by a.id) as abc from
(
select *,sum(case when salary is null then 0 else 1 end)over(order by id) as value from test)a
output:
id name salary Value abc
1 A 4000 1 4000
2 B 1 4000
3 C 1 4000
4 C 1 4000
5 D 2000 2 2000
6 E 2 2000
7 E 2 2000
8 F 1000 3 1000
9 G 2000 4 2000
10 G 3000 5 3000
11 G 5000 6 5000
12 G 6 5000
来源：https://stackoverflow.com/questions/7045040/replace-null-values-with-latest-non-null-value-in-resultset-series-sql-server-2