How to take the first from each customer

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How to take the first from each customer

Author

Topic

amarundo
Starting Member

9 Posts

Posted - 2012-01-04 : 17:13:18

Hi,

I have a TABLE (really it's the result of a select statement) that has something like this:
Customer ID, Order Amount, Order Date
and may have multiple entries per customer.

I'm interested in SELECTing the first occurrence of each Customer Id, and ignoring the rest.

How do I do that?

Thanks.

sunitabeck
Master Smack Fu Yak Hacker

5155 Posts

Posted - 2012-01-04 : 17:20:50

How do you define first? For example, if you want the row with the earliest Order Date then you could do this:


select
   CustomerID,
   OrderAmount,
   OrderDate
from
(
   select
      CustomerID,
      OrderAmount,
      OrderDate,
      row_number() over (partition by CustomerID order by OrderDate) as RN
   from
      YourTable
) s
where
   RN = 1;

X002548
Not Just a Number

15586 Posts

Posted - 2012-01-04 : 17:27:22

I gotta do a perf test

Is that really better than WHERE EXISTS?

Brett

8-)

Hint: Want your questions answered fast? Follow the direction in this link
http://weblogs.sqlteam.com/brettk/archive/2005/05/25/5276.aspx

Want to help yourself?

http://msdn.microsoft.com/en-us/library/ms130214.aspx

http://weblogs.sqlteam.com/brettk/

http://brettkaiser.blogspot.com/

sunitabeck
Master Smack Fu Yak Hacker

5155 Posts

Posted - 2012-01-04 : 19:58:51

quote:
Originally posted by X002548

I gotta do a perf test

Is that really better than WHERE EXISTS?

Brett

Do you mean "where exists" against a subquery where you pick the min value (or using some other method)? Or something else?

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