Product pairs most often bought together

Table order_items:

(order_id, product_id) is unique. Find the 3 pairs of products that appear together in the most orders. A pair is two different products in the same order, written with the smaller id first, and counted once per order.

Sort by number of orders (highest first), then by product_a, then product_b. Return at most 3 rows.

Output columns: product_a, product_b, order_count.

CREATE TABLE order_items (
  order_id int NOT NULL,
  product_id int NOT NULL,
  PRIMARY KEY (order_id, product_id)
);