T-SQL排名帶第一，最小，最大，最後一個

Question

嗨！我有一個包含以下字段的SQL Server表：

DateTime DATETIME 
Price FLOAT 

該表具有唯一的DateTime鍵。我想編寫一個查詢，以20行塊的形式返回數據，返回每行20行的FIRST，MAX，MIN和LAST Price。

在這方面的任何幫助，將greately感激...

Answer 1

我相信你的第一組只包含19行，而不是20行（因爲行號從1開始，而不是0）。這很容易修復 - 只需從ROW_NUMBER（）中減去1即可。

我也在下面提供了一個替代解決方案，可能會更有效率（因爲它沒有子查詢來實現爲嵌套循環），並且它也可能更易於管理。注：如果「價格」中的行數不能被20整除，那麼Sam和我的解決方案將返回一個組中少於20個項目的首次，最小，最大和最後價格 - 該組別包含最近的項目。 （這是測試用的行數不整除20的這樣的查詢是個好主意......）

DECLARE @groupsize INT = 20; 
WITH PricesWithRkGp(PurchaseDate,Price,RkUp,RkDn,Gp) AS (
    SELECT 
    PurchaseDate, 
    Price, 
    -1+ROW_NUMBER() OVER (ORDER BY PurchaseDate), 
    -1+ROW_NUMBER() OVER (ORDER BY PurchaseDate DESC), 
    (-1+ROW_NUMBER() OVER (ORDER BY PurchaseDate))/@groupsize 
    FROM Prices 
) 
    SELECT 
    MIN(Price) AS MinPrice, 
    MAX(Price) AS MaxPrice, 
    Gp, 
    MAX(CASE WHEN RkUp%@groupsize = 0 THEN Price ELSE NULL END) AS FirstPrice, 
    MAX(CASE WHEN RkUp%@groupsize = @groupsize - 1 OR RkDn = 0 THEN Price ELSE NULL END) AS LastPrice 
    FROM PricesWithRkGp 
    GROUP BY Gp 
    ORDER BY Gp; 

Answer 2

你的意思是這樣的：

select 
    *, 
    (select Price from Prices where PurchaseDate = [Start]) as [First Price], 
    (select Price from Prices where PurchaseDate = [Finish]) as [Last Price] 
from 
(
    select 
     MIN(PurchaseDate) as [Start], 
     MAX(PurchaseDate) as [Finish], 
     MIN(Price) as [Min Price], 
     MAX(Price) as [Max Price], 
     AVG(Price) as [Average Price] 
     from 
    (
     select (ROW_NUMBER() OVER (ORDER BY PurchaseDate))/20 as [Seq], * 
     from Prices 
    ) as X 
    group by X.Seq 
) as Y 

請注意，我用下面生成的數據：

create table Prices (
PurchaseDate DATETIME primary key, 
Price FLOAT 
) 

go 

declare @records int 
declare @date datetime 
declare @price float 

set @records = 1000 

while @records > 0 
begin 

    set @date = GETDATE() - cast((RAND() * 10000) as int) 
    set @price = RAND() * 10000  

    if not exists(select 1 from Prices where PurchaseDate = @date) 
    begin 
     insert Prices values (@date, @price) 
     set @records = @records - 1 
    end 
end 

Answer 3

你可以做CTE的這種使用ROW_NUMBER功能。下面是詳細的代碼：

http://blog.sqlauthority.com/2007/06/11/sql-server-2005-t-sql-paging-query-technique-comparison-over-and-row_number-cte-vs-derived-table/