在where子句中使用'case expression column'

SELECT 
    customer_id,
    first_name,
    last_name,
    order_count,
    total_spent,
    CASE 
        WHEN total_spent > 1000 THEN 'VIP'
        WHEN total_spent > 500 THEN 'Regular'
        ELSE 'New'
    END AS customer_type
FROM (
    SELECT 
        c.customer_id,
        c.first_name,
        c.last_name,
        COUNT(o.order_id) AS order_count,
        SUM(o.total_amount) AS total_spent
    FROM customers c
    LEFT JOIN orders o ON c.customer_id = o.customer_id
    GROUP BY c.customer_id, c.first_name, c.last_name
) AS customer_summary
WHERE customer_type = 'VIP';