finding products that customers bought together

Question

I am using PHP and MySQL If I have the following two tables

orders
----
|id|
|--|
|1 |
|2 |
|3 |
|4 |
----

items
----
|order_id|sku|
|------------|
|   1            


        

Answer 1

Try the following:

SELECT c.original_SKU, c.bought_with, count(*) as times_bought_together
FROM (
  SELECT a.sku as original_SKU, b.sku as bought_with
  FROM items a
  INNER join items b
  ON a.order_id = b.order_id AND a.sku != b.sku) c
GROUP BY c.original_SKU, c.bought_with

Answer 2

Here is a flat solution without the subquery:

SELECT a.sku AS original_SKU, b.sku AS bought_with, count(*) as times_bought_together
FROM items AS a
INNER JOIN items AS b ON a.order_id = b.order_id
AND a.sku != b.sku
GROUP BY a.sku