INSERT with ON CONFLICT Upsert

INSERT INTO products (product_id, product_name, unit_price, stock_quantity, category_id)
VALUES
    (101, 'Wireless Mouse', 29.99, 150, 1),
    (102, 'USB Keyboard', 49.99, 80, 1),
    (103, 'HD Monitor', 299.99, 25, 1),
    (104, 'Webcam', 89.99, 60, 1)
ON CONFLICT (product_id)
DO UPDATE SET
    product_name = EXCLUDED.product_name,
    unit_price = EXCLUDED.unit_price,
    stock_quantity = products.stock_quantity + EXCLUDED.stock_quantity
WHERE products.unit_price != EXCLUDED.unit_price
   OR products.stock_quantity < EXCLUDED.stock_quantity;

-- Insert from a SELECT query
INSERT INTO order_summary (order_id, total_items, total_amount)
SELECT
    order_id,
    SUM(quantity) AS total_items,
    SUM(quantity * unit_price) AS total_amount
FROM order_items
GROUP BY order_id
ON CONFLICT (order_id) DO NOTHING;