Question

I have 2 tables: members, orders.

Members: MemberID, DateCreated
Orders:  OrderID, DateCreated, MemberID

I want to find out the number of new members in a given month broken down into number of order groups, eg. 5+, 4, 3, 2, 1, 0

I’ve got the query to work out the number of orders for a member but how can I get these values in one query?

SELECT
  COUNT(o.orderid) AS Purchases
FROM
  members m
  LEFT JOIN orders o ON o.memberid = m.memberid
    AND MONTH(o.DateCreated) = 8
WHERE
  MONTH(m.DateCreated) = 8
GROUP BY
  m.memberid
ORDER BY
  COUNT(o.orderid) DESC

Answer 1

There’s a couple ways you can do this, some of which could be fairly complicated.

This is the way I would do, focusing on the new member part rather than the count part:

  SELECT COUNT(M.MemberID),
         (SELECT COUNT(*) FROM Orders O WHERE O.MemberId = M.MemberId AND O.DateCreated BETWEEN '2010-08-01' AND DATE_ADD('2010-08-01', INTERVAL 1 MONTH)) AS num_orders
    FROM Members M
   WHERE M.DateCreated BETWEEN '2010-08-01' AND DATE_ADD('2010-08-01', INTERVAL 1 MONTH)
GROUP BY num_orders

I did the lookup with dates because it would be faster (it could make use of an index whereas MONTH(M.DateCreated) would always do a full table scan, but you can change it back if really do need all orders/members from a given month).

EDIT:
I forgot to handle the 5+ part of the question so here’s an option for that:

  SELECT COUNT(M.MemberID),
         (SELECT IF(COUNT(*) >= 5, '5+', COUNT(*)) FROM Orders O WHERE O.MemberId = M.MemberId AND O.DateCreated BETWEEN '2010-08-01' AND DATE_ADD('2010-08-01', INTERVAL 1 MONTH)) AS num_orders
    FROM Members M
   WHERE M.DateCreated BETWEEN '2010-08-01' AND DATE_ADD('2010-08-01', INTERVAL 1 MONTH)
GROUP BY num_orders