Show order ids and the number of products in each order.
SELECT order_id ,  count(DISTINCT product_id) FROM Order_items GROUP BY order_id
SELECT order_id ,  count(DISTINCT product_id) FROM Order_items GROUP BY order_id
[{'order_id': 1, 'count(DISTINCT product_id)': 2}, {'order_id': 2, 'count(DISTINCT product_id)': 1}, {'order_id': 4, 'count(DISTINCT product_id)': 3}, {'order_id': 10, 'count(DISTINCT product_id)': 1}, {'order_id': 12, 'count(DISTINCT product_id)': 1}, {'order_id': 13, 'count(DISTINCT product_id)': 3}, {'order_id': 14, 'count(DISTINCT product_id)': 1}, {'order_id': 15, 'count(DISTINCT product_id)': 2}]