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MAX of two columns in one SQL

Posted on 2014-03-09
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Last Modified: 2014-03-09
Hello,
I have the following Customer table:

Table structure
The desired output is:
CustomerId = 1
OrderDate = 02-FEB-2014
CustomerEmail = angel@yahoo.com

I need to get the latest order date and related email from this table.

I tried to do the following:
Select CustomerId, MAX(OrderDate) OVER (PARTITION BY CustomerID), MAX(CustomerEmail) OVER (PARTITION BY CustomerId)
FROM Customer table;

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Though this sql is returning the MAX(orderDate) correctly, the MAX(CustomerEmail) returned is not the one associated to the Max(orderdate) but the one with highest alphabetical order (i.e, in this case Zy2013@yahoo.com).

How do I get both the MAX(OrderDate) and its associated CustomerEmail in the same query using MAX as well as OVER PARTITION by approach?


Thanks!
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Question by:sath350163
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4 Comments
 
LVL 10

Expert Comment

by:aboo_s
ID: 39915785
Select CustomerId, MAX(OrderDate),CustomerEmail  OVER (PARTITION BY OrderDate), FROM Customer table;
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LVL 7

Accepted Solution

by:
Anoo S Pillai earned 1000 total points
ID: 39916033
If my understanding is correct, your logical requirement is to identify latest order by each customer and then get the related value.  So partition by should be based on CustomerID and OrderBy should be based on orderDate
 
ROW_number is the proper function for this requirement, something similar to the following would be useful.

select * 
from 
   (  select * , 
       row_number () over ( partition by customerid order by orderdate desc )  as rownum 
       from customer
  ) DTab
where rownum = 1 

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0
 
LVL 75

Expert Comment

by:Anthony Perkins
ID: 39916037
There are a couple of ways of doing that this is one:
SELECT  c.CustomerId, c.OrderDate, c.CustomerEmail
FROM    [Customer table] c
        INNER JOIN (SELECT  CustomerId,
                            MAX(OrderDate) LastOrderDate
                    FROM    [Customer table]
                    GROUP BY CustomerId
                   ) d ON c.CustomerId = d.CustomerId
                          AND c.OrderDate = d.LastOrderDate

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0
 
LVL 75

Assisted Solution

by:Anthony Perkins
Anthony Perkins earned 1000 total points
ID: 39916049
Here is another approach using a CTE:
;WITH    CTE
          AS (SELECT    CustomerId,
                        OrderDate,
                        CustomerEmail,
                        ROW_NUMBER() OVER (PARTITION BY CustomerId ORDER BY OrderDate DESC) Row
             )
SELECT  CustomerId,
        OrderDate,
        CustomerEmail
FROM    CTE
WHERE   Row = 1

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