How to get the latest row from table using JOIN

Question

I have a join of 5 tables to get the tasks posted by each member having about 15 columns. But for sample code I have taken just two tables of them.

SELECT TOP 5 
    dbo.MemberMst.MemberID, dbo.MemberMst.fname, 
    dbo.TaskMst.TaskMstID, dbo.TaskMst.OnDate, dbo.TaskMst.Description
FROM   
    dbo.MemberMst 
LEFT JOIN
    dbo.TaskMst ON dbo.MemberMst.MemberID = dbo.TaskMst.MemberID

Output is:

MemberID fname  TaskMstID    OnDate                   Description
3    Ursula     NULL         NULL                      NULL
84   Opeyemi    30           2012-09-18 00:00:00.000     asd
85   test       21           2012-09-18 10:30:46.900     aaa
85   test       22           2012-09-18 10:31:04.967     eeee
85   test       23           2012-09-18 10:31:26.640     vvvv

Here in above query I get 3 rows for MemberID=85 who posted 3 tasks but I need only one task from that member which is the latest. How to get the latest task posted by a member so that result would be:-

MemberID fname  TaskMstID OnDate                Description
3    Ursula     NULL      NULL                   NULL
84   Opeyemi    30        2012-09-18 00:00:00.000   asd
85   test       23        2012-09-18 10:31:26.640   vvvv

I mean to say just only one record for each memberID having tasks?

Help appreciated..!

Thanks in advance...!

Answer 1

Since you are using SQL Server 2008, you can take advantage of Window Functions.

Try something like this:

SELECT  c.MemberID, c.fname, c.TaskMstID, c.OnDate, c.Description
FROM
    (
        SELECT  a.MemberID, a.fname,
                b.TaskMstID, b.OnDate, b.Description,
                ROW_NUMBER() OVER (Partition BY a.MemberID ORDER BY b.OnDate DESC) RN
        FROM    MemberMst a
                LEFT JOIN TaskMst b
                    ON a.MemberID = b.MemberID
    ) c
WHERE c.RN = 1

Answer 2

;With Cte1  AS
(

SELECT  top 5 dbo.MemberMst.MemberID, dbo.MemberMst.fname, dbo.TaskMst.TaskMstID, dbo.TaskMst.OnDate, dbo.TaskMst.Description
FROM   dbo.MemberMst left JOIN
dbo.TaskMst ON dbo.MemberMst.MemberID = dbo.TaskMst.MemberID
),
Cte2 As
(   SELECT Rn = Row_Number() Over(Partition by MemberId Order By OnDate Desc), *
    From Cte1

)
Select * 
From Cte2 
Where Rn = 1

Should do the task for you. Try it out.