按日期计算列值的范围

Question

我想根据日期计算product_mrp的最大差值。为此，我试图按日期分组，但此后无法获得。

输入：

+-------------+--------------------+
| product_mrp |     order_date     |
+-------------+--------------------+
|         142 |         01-12-2019 |
|          20 |         01-12-2019 |
|          20 |         01-12-2019 |
|         120 |         01-12-2019 |
|          30 |         03-12-2019 |
|          20 |         03-12-2019 |
|          45 |         03-12-2019 |
|         215 |         03-12-2019 |
|          15 |         03-12-2019 |
|          25 |         07-12-2019 |
|           5 |         07-12-2019 |
+-------------+--------------------+

期望的输出：

 +-------------+--------------------+
| product_mrp |     order_date     |
+-------------+--------------------+
|         122 |         01-12-2019 |
|         200 |         03-12-2019 |
|          20 |         07-12-2019 |
+-------------+--------------------+

Answer 1

您需要将表与其自身连接到order_date列，并计算product_mrp之间的差。然后将其分组并获得最大值。

SELECT MAX(t1.product_mrp - t2.product_mrp) AS product_mrp, t1.order_date
FROM yourTable AS t1
JOIN yourTable AS t2 ON t1.order_date = t2.order_date AND t1.product_mrp >= t2.product_mrp
GROUP BY t1.order_date