Question

I am working on an mySQL assignment for school and I am stuck on a question. I am still new to mySQL. COUNT(o.customer_id) is not working the way I want. I want it to count the number of orders but it is counting all items. i.e. Customer 1 has 2 orders but it is returning 3 because one order has two items. I have three tables one with customers, another with orders than another with each item on each order. Ive posed my query below. Any help would be great.

SELECT email_address, COUNT(o.order_id) AS num_of_orders,
       SUM(((item_price - discount_amount) * quantity)) AS total
FROM customers c JOIN orders o
      ON c.customer_id = o.customer_id
     JOIN order_items ot
      ON o.order_id = ot.order_id
GROUP BY o.customer_id
HAVING num_of_orders > 1
ORDER BY total DESC;

Answer 1

As simple as use Distinct reserved word:

SELECT email_address, COUNT(distinct o.order_id) AS num_of_orders