3.6.3 每列的最大值
任务：找到每种商品的最高价格。
SELECT article, MAX(price) AS price
FROM shop
GROUP BY article
ORDER BY article;
+---------+-------+
| article | price |
+---------+-------+
| 0001 | 3.99 |
| 0002 | 10.99 |
| 0003 | 1.69 |
| 0004 | 19.95 |
+---------+-------+