Given the table below, called 'orders', write code to show the average revenue by month by channel. The format of the result should look like the following:
| Month | Channel | Avg. Revenue |
|---|
Table: orders
| order_id | channel | date | month | revenue |
|---|---|---|---|---|
| 0 | 1 | Online | 2018-09-01 | 09 |
| 1 | 2 | Online | 2018-09-03 | 09 |
| 2 | 3 | In_store | 2018-10-11 | 10 |
| 3 | 4 | In_store | 2018-08-21 | 08 |
| 4 | 5 | Online | 2018-08-13 | 08 |
| 5 | 6 | Online | 2018-10-29 | 10 |