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  2. MIDRANGE-L
  3. September 2001

RE: Elementary SQL question

>> From: Matthias Oertli
>>
>> Given a customer master file (one record per customer) and a
>transaction
>> file (one record per transaction, one customer can have many
>> transactions), how would it be possible to find the average number of
>> transactions per customer with one single SQL statement?

>You need count(*) of the transaction file divided by count(*) of the
>customer master.  I can't see any way of doing that in one statement.

I guess I don't understand what is being asked.  If I do a count of
transactions divided by a count of masters, doesn't that do funny things if
say, all the transactions belong to one master?

Here's my submission:

select avg(count) from
  (select count(*) as count from transactionfile
     group by customernumber) as average

  --buck

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