你好，这是我的疑问：
MariaDB [PV_Anlage]>
SELECT created_at, verbrauch_ges
FROM pv_metrics
group by DATE(created_at)
ORDER BY ID DESC limit 20;
+---------------------+---------------+
| created_at | verbrauch_ges |
+---------------------+---------------+
| 2025-03-23 00:00:04 | 5628.79 |
| 2025-03-22 00:00:06 | 5622.54 |
| 2025-03-21 00:00:11 | 5615.44 |
| 2025-03-20 00:00:13 | 5609.49 |
| 2025-03-19 00:00:17 | 5605.4 |
| 2025-03-18 00:00:00 | 5600.45 |
| 2025-03-17 00:00:03 | 5591.36 |
| 2025-03-16 00:00:09 | 5585.2 |
| 2025-03-15 00:00:16 | 5578.96 |
| 2025-03-14 00:00:04 | 5571.1 |
| 2025-03-13 00:00:07 | 5560.34 |
| 2025-03-12 00:00:10 | 5550.54 |
| 2025-03-11 00:00:13 | 5540.12 |
| 2025-03-10 00:00:16 | 5534.81 |
| 2025-03-09 00:00:18 | 5528.48 |
| 2025-03-08 00:00:17 | 5521.71 |
| 2025-03-07 00:00:11 | 5515.27 |
| 2025-03-06 00:00:14 | 5510.17 |
| 2025-03-05 00:00:06 | 5504.08 |
| 2025-03-04 00:00:09 | 5497.21 |
+---------------------+---------------+
这是结果，因为我每 20 秒写入一次值。我选择了当天的第一个值，所以现在我需要天数之间的差异。我尝试使用 LAG() 函数，但我不知道如何将该函数纳入常规查询。
最好的问候弗兰克