是连接这些子查询的更好方法吗？

SELECT order_id, customer_name
FROM orders
WHERE customer_id IN (SELECT customer_id FROM customers WHERE country = 'USA');

SELECT o.order_id, c.customer_name
FROM orders o
JOIN customers c ON o.customer_id = c.customer_id
WHERE c.country = 'USA';

SELECT customer_id
FROM customers c
WHERE EXISTS (SELECT 1 FROM orders o WHERE o.customer_id = c.customer_id);

WITH customer_orders AS (
    SELECT customer_id, SUM(amount) as total_amount
    FROM orders
    GROUP BY customer_id
)
SELECT c.customer_name, co.total_amount
FROM customers c
JOIN customer_orders co ON c.customer_id = co.customer_id;

SELECT order_id, amount
FROM orders
WHERE amount > (SELECT AVG(amount) FROM orders);

SELECT order_id, amount
FROM orders o1
JOIN (SELECT AVG(amount) as avg_amount FROM orders) o2
ON o1.amount > o2.avg_amount;