Question

I am running a MySQL database in rails 2.3. my model associations that I am interacting with in this query are as follows:

models: users and orders

users have 1 email

users have many orders

orders have a created at date

I want to make a list of emails from all users who have at least one order with the latest order being at least 3 months old (so, lets say today is feb 24th 2012, the last order was placed on nov 24th 2011 or earlier)

I know how to grab orders created on or before nov 24th with this query:

SELECT * FROM orders WHERE created_at <= "2011-11-24 00:00:00.000000 -08:00"

I don’t know how to find users with at least 1 order AND have those conditions for each order.

Any help would be greatly appreciated!

Answer 1

SELECT users.email
FROM users
  JOIN
    ( SELECT user_id, MAX(created_at) AS created_at
      FROM orders
      GROUP BY user_id
      HAVING MAX(created_at) < CURDATE() - INTERVAL 3 MONTH
    ) AS oo
    ON oo.user_id = users.id
ORDER BY oo.created_at DESC