SQL Server query to join two tables

Question

I've got a 2 part problem where through the use of google managed to find the answer to the first part at SQL get the last date time record

User Osy code work really well for me,

Osy's code below!

 select filename, dates, status 
 from yt a 
 where a.dates = (select max(dates)
                  from yt b
                  where a.filename = b.filename)

The query returns only the latest dates for each filename.

If I could just stick to the same example question as url above.

This is the table used in the example:

yt table:

+---------+------------------------+-------+
|filename |Dates                   |Status |
+---------+------------------------+-------+
|abc.txt  |2012-02-14 12:04:45.397 |Open   |
|abc.txt  |2012-02-14 12:14:20.997 |Closed |
|abc.txt  |2013-02-14 12:20:59.407 |Open   |
|dfg.txt  |2012-02-14 12:14:20.997 |Closed |
|dfg.txt  |2013-02-14 12:20:59.407 |Open   |
+---------+------------------------+-------+

The second part of the problem:

What I am now trying to achieve is that I have a second table and would like to join the results from the query above on the filename and return the user.

Table2

+--------+--------+
|filename |ref     |
+---------+--------+
|abc.txt  |Heating |
|dfg.txt  |Cooling |
+---------+---- ---+

Result that I am trying to achieve from the query is as follows, using Osy's code above to return only the latest for each entry per device, and then to display the ref column and not display the filename

Example:

+---------+------------------------+-------+
|ref      |Dates                   |Status |
+---------+------------------------+-------+
|Heating  |2013-02-14 12:20:59.407 |Open   |
|Cooling  |2013-02-14 12:20:59.407 |Open   |
+---------+------------------------+-------+

I can use a inner join directly on the yt table but cannot get is to combine (nest) with the code from Osy above.

Using SQL Server 2012. Please let me know if I left out anything.

Thank you.

Answer 1

This might be faster way to do it.

SELECT  [ref],
        [dates],
        [status]
 FROM   (SELECT a.[filename],
                a.[dates],
                a.[status],
                t2.[ref],
                ROW_NUMBER() OVER (PARTITION BY a.[filename] ORDER BY a.[dates] DESC) [Rn]
         FROM   yt a
                JOIN Table2 t2 ON a.[filename] = t2.[filename]
        ) t
 WHERE  t.Rn = 1        

Answer 2

Continuing with your posted example code, again perform one more JOIN with Table2 like

select t2.ref, xx.Dates, xx.Status
from Table2 t2 join (
select filename, dates, status 
 from yt a where a.dates = (
 select max(dates)
 from yt b
 where a.filename = b.filename
)) xx on t2.filename = xx.filename;

Answer 3

Speculating the bottom query but is should work:

SELECT a.ref, MAX(b.Dates), b.Status
FROM Table2 AS a INNER JOIN yt AS b ON a.ref=b.filename AND b.Status='Open'
GROUP BY a.ref, b.Status

Let me know if it works