| 年度 | 月度 | 离职数 |
+--------+--------+-----------+
| 2009 | 1 | 7 |
| 2009 | 2 | 4 |
| 2009 | 3 | 8 |
| 2009 | 4 | 10 |
| 2009 | 5 | 16 |
| 2009 | 6 | 4 |
| 2009 | 7 | 6 |
| 2009 | 8 | 9 |
| 2009 | 9 | 4 |
| 2009 | 10 | 9 |
| 2009 | 11 | 10 |
https://blog.csdn.net/weixin_42642782/article/details/112479016
select T2.月度,(T2.离职数 - T1.离职数)/T1.离职数 from 表 T1, 表 T2
where T1.月度 = T2.月度-1