如何通过日期从另一个表中选择最新的项目

Question

I have two tables Projects and Plans, and I need get recent projects from the last plan by create date:

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

I wrote query that take single project from the last plan, but i can't write query to get many projects by single query.

Here my query:

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

Desired result is (all projects from the last plans):

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

UPDATE: Gordon Linoff gave the good answer, but it wasn't solved my question, because both his queries don't take '00003' project (its last plan is '00001').

I wrote my query with ' OVER Clause ' (Stanislovas Kalašnikovas note about it).

So I post full answer that solves my question for future googlers:

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

You can use a subquery to get the most recent plan. Then just join this to projects:

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'

An alternative method is to just use 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

This is example of ROW_NUMBER with 1 table, easy you can use It in your case.

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

you can use datediff() eg if you want to take the entries of last 10 days use:

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