如何通過日期從另一個表中選擇最新的項目

Question

我有兩個表“項目”和“計划”，我需要按創建日期從上一個計划中獲取最近的項目：

Projects:
ProjectId, PlanId, StartDate, EndDate 
(guid)     (guid)  (datetime) (datetime)
-------------------------------------
00001,     00001,  1/1/2015   31/1/2015   
00001,     00002,  3/2/2015   15/2/2015   
00002,     00001,  1/2/2015   20/2/2015   
00002,     00002,  1/2/2015   21/2/2015   
00003,     00001,  1/3/2015   10/3/2015   

Plans:
PlanId, CreateDate
(guid)  (datetime)
--------------------
00001,   1/1/2015
00002,   5/2/2015

我寫了從上一個計划中提取單個項目的查詢，但是我無法通過單個查詢編寫查詢來獲取多個項目。

這是我的查詢：

SELECT TOP 1 pr.ProjectId,
        pl.CreateDate,
        pr.StartDate,
        pr.EndDate
FROM   Projects pr
        INNER JOIN Plans pl
            ON  pr.PlanId = pl.PlanId
WHERE ProjectId = '000002'
ORDER BY pl.CreateDate DESC

所需的結果是（來自上一個計划的所有項目）：

ProjectId, PlanId, StartDate, EndDate
--------------------------------------
00001,     00002,  3/2/2015,  15/2/2015
00002,     00002,  1/2/2015,  21/2/2015
00003,     00001,  1/3/2015,  10/3/2015

更新：戈登·利諾夫（Gordon Linoff）給出了很好的答案，但這並沒有解決我的問題，因為他的兩個查詢都沒有采用“ 00003”項目（其最后一個計划是“ 00001”）。

我用“ OVER Clause ”（StanislovasKalašnikovas的注釋）寫了我的查詢。

因此，我發布了完整的答案，為以后的Google員工解決了我的問題：

SELECT * FROM
    (SELECT 
        result.ProjectId, 
        result.CreateDate, 
        result.StartDate, 
        result.EndDate, 
        ROW_NUMBER() OVER (PARTITION BY ProjectId ORDER BY CreateDate DESC) AS RowNumber
    FROM ( 
            SELECT  pr.ProjectId AS ProjectId,
                    pl.CreateDate AS CreateDate,
                    pr.StartDate AS StartDate,
                    pr.EndDate AS EndDate
            FROM   Projects pr
            INNER JOIN Plans pl ON  pr.PlanId = pl.PlanId
            --WHERE ProjectId IN ('000001', '000003') --Filter
         ) AS result
) AS result
WHERE result.RowNumber = 1

Answer 1

您可以使用子查詢來獲取最新計划。 然后將其加入項目：

SELECT pr.ProjectId, pl.CreateDate, pr.StartDate, pr.EndDate
FROM (SELECT TOP 1 pl.*
      FROM plans pl
      ORDER BY pl.CreateDate DESC
     ) pl JOIN
     Projects pr
     ON pr.PlanId = pl.PlanId;
WHERE ProjectId = '000002'

另一種方法是只使用TOP WITH TIES ：

SELECT TOP 1 WITH TIES pr.ProjectId, pl.CreateDate, pr.StartDate, pr.EndDate
FROM plans pl
     Projects pr
     ON pr.PlanId = pl.PlanId;
WHERE ProjectId = '000002'
ORDER BY pl.CreateDate DESC

Answer 2

這是帶有1個表的ROW_NUMBER示例，很容易在您的情況下使用它。

CREATE TABLE #Test
(
Id NVARCHAR(100),
Data DATE
)

INSERT INTO #Test VALUES ('1', '2015-01-04'), ('1', '2015-01-07'), ('2', '2015-01-05'), ('2', '2015-01-08')

SELECT Id, Data
FROM (
    SELECT Id, Data, ROW_NUMBER() OVER (PARTITION BY Id ORDER BY Data DESC) rn
    FROM #Test
    )x
WHERE rn > 1


DROP TABLE #Test

Answer 3

您可以使用datediff（）例如，如果您想獲取最近10天的條目，請使用：

SELECT  pr.ProjectId,
        pl.CreateDate,
        pr.StartDate,
        pr.EndDate
FROM   Projects pr
        INNER JOIN Plans pl
            ON  pr.PlanId = pl.PlanId
WHERE datediff(day,pl.CreateDate,getdate())<10