如何返回最近的记录

Question

I have two tables, Sales and SalesNotes , as below

Sales
SO No......Cust.........Date  
1..........Me..........22-04-13  
2..........You.........23-04-13  



SalesNotes  

SO No.......Note.......Notedate  
1...........Blah.......24-04-13  
2...........Bleh.......23-04-13  
2...........Bluh.......27-04-13  

How can I return a result set showing Cust, date and the most recent dated note for the corresponding SO no?

I have tried using MAX() but cannot use an aggregate in the where clause and do not understand how I could implement HAVING to do what I need.

What I am trying to achieve is:

SO No.......Cust........Note  
1...........Me..........Blah    
2...........You.........Bluh  

Answer 1

One way of doing this is with the row_number window function:

SELECT    s.[So no], [cust], [Note]
FROM      [Sales] s
LEFT JOIN (SELECT [So no], [Note],
                  ROW_NUMBER() OVER (PARTITION BY [So no]
                                     ORDER BY [Notedate] DESC) rn
           FROM   [SalesNotes]) n ON s.[So no] = n.[So no] AND rn = 1

Answer 2

You can use outer apply for this:

select s.*, sn.note
from sales s outer apply
     (select top 1 sn.*
      from salesnotes sn
      where sn.so_no = s.so_no
      order by sn.notedate desc
     ) sn;

Answer 3

You can use window function FIRST_VALUE to get the most recent Note value per [SO No.] :

SELECT s.[SO No.], Cust, Note
FROM Sales AS s
INNER JOIN (SELECT DISTINCT [SO No.], 
                   FIRST_VALUE(Note) OVER (PARTITION BY [SO No.] 
                                           ORDER BY NoteDate DESC) AS Note
            FROM SalesNotes) AS sn
ON s.[SO No.] = sn.[SO No.]

This way you avoid using a correlated subquery, which, I think, is less performant.

FIRST_VALUE is available from SQL Server 2012+.

Answer 4

I understand your output as last sale and last note for that sale. If you want to do this for all sales, just remove first Top 1 .You can do it with Apply :

Select Top 1 s.SoNo, s.Cust, oa.Note
From Sales s
Outer Apply (Select Top 1 Note From Notes n Where n.SoNo = s.SoNo Order By Date Desc) oa
Order By s.Date desc

Answer 5

Something like this:

select s.so_no, s.cust, 
(select top (1) n.note from salesnotes n where s.so_no = n.so_no order by notedate desc) as note
from sales s

Answer 6

Since you were talking about 'max' in where clause , this is just for you to understand 'max' . And just so you know this is not a good solution because there are number of problems like what if notes are same for two different customer, what if customers have the same name and so on and so forth. You should follow the outer apply concept as others have suggested for the right solution .

Select s.SoNo, s.cust, sn.notes,           max(sn.noteDate) from sales s inner join salesnotes sn on s.sono=sn.sono group by s.sono,s.cust,sn.notes