Question

I have a table of orders that I know have duplicates

    customer   order_number   order_date
   ----------  ------------   -------------------
          1             1     2012-03-01 01:58:00
          1             2     2012-03-01 02:01:00
          1             3     2012-03-01 02:03:00
          2             4     2012-03-01 02:15:00
          3             5     2012-03-01 02:18:00
          3             6     2012-03-01 04:30:00
          4             7     2012-03-01 04:35:00
          5             8     2012-03-01 04:38:00
          6             9     2012-03-01 04:58:00
          6            10     2012-03-01 04:59:00

I want to find all duplicates (order by same customer within 60 minutes of eachother). Either a resultset consisting of the ‘duplicate’ rows or a set of all customers with a count of how many duplicates.

Here is what I have tried

SELECT
   customer,
   count(*)
FROM
   orders
GROUP BY
   customer,
   DATEPART(HOUR, order_date)
HAVING (count(*) > 1)

This doesn’t work when duplicates are within 60 minutes of each other but are in different hours i.e 1:58 and 2:02

I’ve also tried this

SELECT
  o1.customer,
  o1.order_number,
  o2.order_number,
  DATEDIFF(MINUTE,o1.order_date, o2.order_date) AS [diff]
FROM
  orders o1 LEFT OUTER JOIN
  orders o2 ON o1.customer = o2.customer AND o1.order_number <> o2.order_number
WHERE
  ABS(DATEDIFF(MINUTE,o1.order_date, o2.order_date)) < 60

Now this gives me all of the duplicates but it also gives me multiple rows per duplicate order. i.e (o1, o2) and (o2, o1) which wouldn’t be so bad if there were’nt some orders with multiple duplicates. In those cases I get (o1, o2), (o1,o3), (o2, o1), (o2, o3), (o3, o1), (o3, o2) etc. I get all of the permutations.

Anyone have some insight? I’m not necessarily looking for the best performing answer here, just one that works.

Answer 1

SELECT
  *,
  CASE WHEN EXISTS (SELECT *
                      FROM orders AS lookup
                     WHERE customer    = orders.customer
                       AND order_date <  orders.order_date
                       AND order_date >= DATEADD(hour, -1, order_date)
                   )
       THEN 'Principle Order'
       ELSE 'Duplicate Order'
  END as Order_Status
FROM
  orders

Using EXISTS and a correlated sub-query you can check if there were any preceding orders in the last hour.