Create a SQL query to retrieve most recent records

问题

I am creating a status board module for my project team. The status board allows the user to to set their status as in or out and they can also provide a note. I was planning on storing all the information in a single table ... and example of the data follows:

Date               User         Status    Notes
-------------------------------------------------------
1/8/2009 12:00pm   B.Sisko      In        Out to lunch    
1/8/2009 8:00am    B.Sisko      In  
1/7/2009 5:00pm    B.Sisko      In    
1/7/2009 8:00am    B.Sisko      In    
1/7/2009 8:00am    K.Janeway    In   
1/5/2009 8:00am    K.Janeway    In    
1/1/2009 8:00am    J.Picard     Out       Vacation

I would like to query the data and return the most recent status for each user, in this case, my query would return the following results:

Date               User         Status    Notes
-------------------------------------------------------  
1/8/2009 12:00pm   B.Sisko      In        Out to lunch    
1/7/2009 8:00am    K.Janeway    In   
1/1/2009 8:00am    J.Picard     Out       Vacation

I am try to figure out the TRANSACT-SQL to make this happen? Any help would be appreciated.

回答1:

Aggregate in a ~~subquery~~ derived table and then join to it.

 Select Date, User, Status, Notes 
    from [SOMETABLE]
    inner join 
    (
        Select max(Date) as LatestDate, [User]
        from [SOMETABLE]
        Group by User
    ) SubMax 
    on [SOMETABLE].Date = SubMax.LatestDate
    and [SOMETABLE].User = SubMax.User

回答2:

another way, this will scan the table only once instead of twice if you use a subquery

only sql server 2005 and up

select Date, User, Status, Notes 
from (
       select m.*, row_number() over (partition by user order by Date desc) as rn
       from [SOMETABLE] m
     ) m2
where m2.rn = 1;

回答3:

The derived table would work, but if this is SQL 2005, a CTE and ROW_NUMBER might be cleaner:

WITH UserStatus (User, Date, Status, Notes, Ord)
as
(
SELECT Date, User, Status, Notes, 
     ROW_NUMBER() OVER (PARTITION BY User ORDER BY Date DESC)
FROM [SOMETABLE]
)

SELECT User, Date, Status, Notes from UserStatus where Ord = 1

This would also facilitate the display of the most recent x statuses from each user.

回答4:

Another easy way:

SELECT Date, User, Status, Notes  
FROM Test_Most_Recent 
WHERE Date in ( SELECT MAX(Date) from Test_Most_Recent group by User)

来源：https://stackoverflow.com/questions/1049702/create-a-sql-query-to-retrieve-most-recent-records

标签

sql

tsql

derived-table