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Field value comparison

Posted on 2014-09-30
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Last Modified: 2014-10-08
Hi,
I have a table with an order no field and an orderdate field. The order field is a far char 50 and the order date Is datetime.  I would like to be able to check to see if there are two  or more of the same orderno  and if so delete all but the most recent of the entries.  
Any help on this would be appreciated
Thanks
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Question by:Morpheus7
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10 Comments
 
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Assisted Solution

by:chaau
chaau earned 125 total points
ID: 40353699
You can easily do this with a window function, like this:
with oo as (
 select *, row_number() over(partition by orderNo order by orderDate DESC) rn
 from orders)
delete from oo where rn > 1

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LVL 26

Assisted Solution

by:Chris Luttrell
Chris Luttrell earned 125 total points
ID: 40353704
Use a CTE and the OVER clause to assign ordered values to each value and then delete those that are not the latest one per Order No.
CREATE TABLE aTable (Order_No INT, Order_Date DATETIME);
GO

INSERT INTO dbo.aTable ( Order_No, Order_Date ) VALUES  ( 100, GETDATE() ), ( 100, GETDATE() - RAND() * 50 );
INSERT INTO dbo.aTable ( Order_No, Order_Date ) VALUES  ( 111, GETDATE() ), ( 111, GETDATE() - RAND() * 50 ), ( 111, GETDATE() - RAND() * 50 ), ( 111, GETDATE() - RAND() * 50 );
INSERT INTO dbo.aTable ( Order_No, Order_Date ) VALUES  ( 222, GETDATE() ), ( 222, GETDATE() - RAND() * 50 ), ( 222, GETDATE() - RAND() * 50 ), ( 222, GETDATE() - RAND() * 50 ), ( 222, GETDATE() - RAND() * 50 );
INSERT INTO dbo.aTable ( Order_No, Order_Date ) VALUES  ( 333, GETDATE() ), ( 333, GETDATE() - RAND() * 50 ), ( 333, GETDATE() - RAND() * 50 );
INSERT INTO dbo.aTable ( Order_No, Order_Date ) VALUES  ( 444, GETDATE() );

SELECT * FROM dbo.aTable AT;

WITH cte AS 
(
SELECT AT.Order_No, AT.Order_Date, ROW_NUMBER() OVER (PARTITION BY AT.Order_No ORDER BY AT.Order_Date DESC) rn 
FROM dbo.aTable AT
)
DELETE
FROM cte
WHERE cte.rn > 1;

SELECT *
FROM dbo.aTable AT;

DROP TABLE dbo.aTable;

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This is the results:Query Results
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Expert Comment

by:Chris Luttrell
ID: 40353706
I am too fancy, someone was quicker with less details :)
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Expert Comment

by:chaau
ID: 40353718
Did it in SQLFiddle
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Assisted Solution

by:Scott Pletcher
Scott Pletcher earned 250 total points
ID: 40355375
Don't think you need to do all that row numbering/counting (1 table scan instead of 2):


DELETE FROM ot
FROM orderstable ot
INNER JOIN (
    SELECT [order no], MAX(orderdate) AS orderdate
    FROM orderstable
    GROUP BY [order no]
    HAVING MIN(orderdate) <> MAX(orderdate)
) AS orders_last ON
    ot.[order no] = orders_last.[order no] AND
    ot.orderdate < orders_last.orderdate
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Expert Comment

by:chaau
ID: 40355572
@Scott: Your query is good, but it will leave duplicate records if there are multiple records with the same max(orderDate) for the orderNo
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LVL 26

Expert Comment

by:Chris Luttrell
ID: 40355598
Scott, I did a profile comparison of my CTE and your nested select and I only see 1 table scan for my solution and 2 table scans with yoursProfile Comparison
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LVL 69

Expert Comment

by:Scott Pletcher
ID: 40355688
Sorry, quite true if there's no covering index for [order no] and orderdate.  I shouldn't have assumed that.

I don't object to your ROW_NUMBER() method anyway since you used:
SELECT AT.Order_No, AT.Order_Date, ROW_NUMBER() OVER
and not
SELECT *, ROW_NUMBER() OVER ...
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Accepted Solution

by:
Scott Pletcher earned 250 total points
ID: 40355694
chaau:

Yeah, I figured you wouldn't get exact same times for the same order no.  If that's possible, use the CTE ... and check your order logic, because you've got a bigger issue than this DELETE!
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LVL 26

Expert Comment

by:Chris Luttrell
ID: 40355699
check your order logic, because you've got a bigger issue than this DELETE!
:-)
True!
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