SELECT
  c.id,
  c.name,
  COUNT(o.id) AS paid_order_count,
  COALESCE(SUM(o.total_amount), 0) AS paid_revenue
FROM customers c
LEFT JOIN orders o
  ON o.customer_id = c.id
 AND o.status = 'paid'
 AND o.created_at >= $1
 AND o.created_at < $2
WHERE c.segment = $3
GROUP BY c.id, c.name
ORDER BY paid_revenue DESC
LIMIT 50;

• 它做了什么：统计指定客户分层在时间窗口内的已支付订单数和收入，并按收入排序。
• 参数：
  • $1：开始时间，含。
  • $2：结束时间，不含。
  • $3：客户分层，例如 enterprise。
• 正确性提醒：时间窗口建议使用半开区间，避免月底/日切时重复计算边界订单。