示例
示例
SELECT city, SUM(amount) AS total, COUNT(*) AS cnt
FROM (
SELECT city, amount FROM orders_2023
UNION ALL
SELECT city, amount FROM orders_2024
) t
GROUP BY city
ORDER BY total DESC;| 合并 | UNION ALL 保留全部分片行，不去重 |
|---|---|
| 聚合 | 外层再 GROUP BY |
| 结构 | 分支列顺序与类型一致，可 CAST 对齐 |