Special Join scenario

Posted on 2010-11-19
Medium Priority
Last Modified: 2012-05-10
I'm trying to find a performant solution for a special JOIN, but don't know how to solve it. This JOIN needs lots of performance and is surely not optimal.

Here it is: For each customer (tblCustomer) there exists a colour, but this colour can change from day to day, and the history of all colours must be tracked. So we have:

tblCustomer: ID
tblColour: IDCustomer, colour, timestamp

What I need is the most current colour for the customer.

So my current JOIN goes like this:

SELECT tblCustomer.ID , C2.colour
FROM  tblCustomer (NOLOCK) JOIN tblColour AS C2 ON tblCustomer.ID = C2.IDCustomer 
          JOIN (SELECT C1.IDCustomer, MAX(C1.timestamp) AS MaxTime FROM tblColour AS C1 GROUP BY C1.IDCustomer) AS T1 ON (T1.MaxTime = C2.timestamp) AND (T1.IDCustomer = C2.IDCustomer)  

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Any idea welcome
Question by:PC-Alex
LVL 143

Assisted Solution

by:Guy Hengel [angelIII / a3]
Guy Hengel [angelIII / a3] earned 1000 total points
ID: 34173344
this article should help you solve the issue:

Expert Comment

ID: 34175049
try this
select t2.ID,t3.Colour from
select t0.ID,max(t1.[timestamp]) as maxtime from tblCustomer t0
inner join tblColour t1 on t0.ID=t1.ID
group by t0.ID
) t2
inner join tblColour t3 on t2.ID=t3.ID
and t2.maxtime=t3.[timestamp]

Expert Comment

ID: 34175108
pretty much what you had, did not see your entire statment.
LVL 58

Accepted Solution

cyberkiwi earned 1000 total points
ID: 34178081
select C.ID, C2.Colour
from tblCustomer C
      select IDCustomer, Colour, rn=row_number() over (partition by IDCustomer order by timestamp desc)
      from tblColour) C2 ON C.ID = C2.IDCustomer and C2.rn=1

Author Closing Comment

ID: 34178611
Thank you guys; I split points, because angel was faster and brought some background, and cyberkiwi took the time to type the solution.

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