Question

Using this query, I get the result I need of how many orders each customer has placed. However, when I use the SUM(OrderLine.ActualPrice) in the SELECT field and use an inner join to link the Order table to the OrderLine table which contains the price. The COUNT results are skewed, as the OrderLine table contains multiple OrderNo of the same Order, since one order can contain multiple products.

How do I keep the COUNT to the result I have with this query, while putting in the SUM query for the Total Purchase Amount of their orders?

SELECT C.custno, 
       companyname, 
       Count(customerorder.orderno)AS 'Total Orders', 
FROM   customer C 
       INNER JOIN customerorder 
               ON customerorder.custno = C.custno 
GROUP  BY C.custno, 
          companyname 

MODIFIED QUERY WITH INCORRECT RESULT

SELECT C.custno, 
       companyname, 
       Count(customerorder.orderno)AS 'Total Orders', 
       Sum(orderline.actualprice) 
FROM   customer C 
       INNER JOIN customerorder 
               ON customerorder.custno = C.custno 
       INNER JOIN orderline 
               ON customerorder.orderno = orderline.orderno 
GROUP  BY C.custno, 
          companyname 

This is the query I tried to use and received the skewed COUNT results.

Answer 1

You have two basic options.

Use DISTINCT

SELECT C.custno, 
       companyname, 
       Count(DISTINCT customerorder.orderno)AS 'Total Orders', 
       Sum(orderline.actualprice) 
FROM   customer C 
       INNER JOIN customerorder 
               ON customerorder.custno = C.custno 
       INNER JOIN orderline 
               ON customerorder.orderno = orderline.orderno 
GROUP  BY C.custno, 
          companyname 

Note:

In a comment on another question you say that this scews te result still. This seems to imply that the same orderno can appear in more than one customerorder record. Is that correct?

Use a sub-query to make the join 1:1 instead of 1:many

SELECT C.custno, 
       companyname, 
       Count(customerorder.orderno)AS 'Total Orders', 
       Sum(orderline.actualprice) 
FROM   customer C 
       INNER JOIN customerorder 
               ON customerorder.custno = C.custno 
       INNER JOIN (SELECT orderno, SUM(actualprice) AS actualprice
                     FROM orderline 
                 GROUP BY orderno)
               ON customerorder.orderno = orderline.orderno 
GROUP  BY C.custno, 
          companyname