SQL Server：表中连续行之间的差

Question

我需要帮助来计算每行数据之间的差异。计数递增，每小时捕获一次数据。

+-------------------------+------------------+
|         t_stamp         |  qty             |
+-------------------------+------------------+
| 2020-01-08 19:00:00.007 |           514096 |
| 2020-01-08 20:00:00.007 |           514096 |
| 2020-01-08 21:00:00.003 |           514096 |
| 2020-01-08 22:00:00.003 |           514096 |
| 2020-01-08 23:00:00.013 |           514096 |
| 2020-01-09 01:00:00.003 |           531181 |
| 2020-01-09 02:00:00.003 |           531181 |
| 2020-01-09 03:00:00.000 |           531181 |
+-------------------------+------------------+

我想返回的是：

+-------------------------+------------------+
|         t_stamp         | count_per_hr     |
+-------------------------+------------------+
| 2020-01-08 19:00:00.007 |                0 |
| 2020-01-08 20:00:00.007 |                0 |
| 2020-01-08 21:00:00.003 |                0 |
| 2020-01-08 22:00:00.003 |                0 |
| 2020-01-08 23:00:00.013 |                0 |
| 2020-01-09 01:00:00.003 |            17085 |
| 2020-01-09 02:00:00.003 |                0 |
| 2020-01-09 03:00:00.000 |                0 |
+-------------------------+------------------+

Answer 1

使用lag()：

select t.*,
       (qty - lag(qty, 1, qty) over (order by t_stamp)) as diff
from t;

请注意，这使用lag()的3参数形式将缺少的先前值（即第一个值）转换为指定值。