SQL：如何按最大日期分组

Question

I'm pretty new to SQL, so please excuse what seems like what should be basic query. I've been searching for and trying to convert other similar answer's code to make mine work, but I just can't seem to get it right.

I have 2 tables. The tables are linked via a unique Employee ID(EMPLID). Table 1(JOB) houses various job related information like title and table 2(TITLE_CHANGES) houses promotion actions, reasons, and dates. I need to develop a query that returns * from both JOB and TITLE_CHANGES tables based on the most recent TITLE_CHANGES date.

FYI this does not mirror my actual table data. I am oversimplifying it to make it easier to explain.

It should return:

EMLPID |     TITLE    |TitleDate   |TitleChnageReason|Requested_Date

12345  |  Specialist 2| 02/01/2015|      Merit       |01/31/2015

JOB table    
  EMPLID    |         Title       | Title Date  
---------+---------------+----------------+  
 12345      |  Specialist 2       | 02/01/2015       
--------+----------------+----------------  
 12345      |  Specialist 1       | 09/01/2014  
--------+----------------+----------------  
 44576      |  Analyst 3          | 05/01/2015  
--------+----------------+----------------  
 44576      |  Analyst 2          | 03/01/2014  
--------+---------------------+-----------  

TITLE_CHANGES Table

  EMPLID    | Title change reason | Requested_Date  
------------+---------------------+----------------+  
 12345      |  Merit              | 01/31/2015  
------------+---------------------+----------------  
 12345      |  Newhire            | 08/30/2014  
------------+---------------------+----------------  
 44576      |  Promotion          | 04/30/2015  
------------+---------------------+----------------  
 44576      |  Newhire            | 02/28/2014  
------------+---------------------+----------------  

Thanks for your help!

Craig

Answer 1

Try this query

SELECT j.EMPLID, 
SUBSTRING_INDEX(GROUP_CONCAT(j.TITLE ORDER BY j.TitleDate DESC),',',1) AS title,
SUBSTRING_INDEX(GROUP_CONCAT(j.TitleDate ORDER BY j.TitleDate DESC),',',1) AS title_date, 
SUBSTRING_INDEX(GROUP_CONCAT(tc.TitleChnageReason ORDER BY tc.Requested_Date DESC),',',1) AS title_change_reson,
SUBSTRING_INDEX(GROUP_CONCAT(tc.Requested_Date ORDER BY tc.Requested_Date DESC),',',1) AS request_date,
FROM JOB j
JOIN TITLE_CHANGES tc ON(tc.EMPLID = j.EMPLID)
GROUP BY j.EMPLID

Answer 2

Try this

SELECT j.emplid AS 'EMPLID', j.title AS 'TITLE', j.title_date AS 'TitleDate', e.reason AS 'TitleChangeReason', q.requested_date AS 'Requested_Date'
FROM
    job j
    INNER JOIN
    (SELECT a.* 
        FROM title_changes a
        INNER JOIN (SELECT emplid, MAX(requested_date) as rd FROM title_changes GROUP BY 1) b 
        ON a.emplid=b.emplid AND a.requested_date=b.rd) 
    e ON j.emplid=e.emplid

Answer 3

选择*从作业j内联接Title_Change tj在j.empid = tj.empid上按j.titledate desc排序

Answer 4

Select Top(1) j.empid, j.title, j.titleDate,tj.TitleChangeReason,tj.Request_Date From job j Inner join Title_Change tj On j.empId= tj.empid Order by j.TitleDate desc

Try this, Thanks.

Answer 5

从JOB j，TITLE_CHANGES tc中选择j.EMPLID，j.Title，j.Title日期，标题更改原因，MAX（tc.Requested_Date），其中j.EMPLID = tc.EMPLID