You are given a table of NVIDIA GPU order transactions and asked to use SQL to analyze business performance. Write a query that returns total revenue by month for completed orders only. The result should show the month in YYYY-MM format and the summed revenue for that month, ordered from highest revenue to lowest.
| Column | Type | Description |
|---|---|---|
| order_idPK | INT | Unique order identifier |
| customer_name | VARCHAR(100) | Customer name |
| product_line | VARCHAR(50) | NVIDIA product line purchased |
| order_date | DATE | Date the order was placed |
| order_status | VARCHAR(20) | Status of the order such as completed or cancelled |
| revenue | DECIMAL(10,2) | Revenue recognized for the order |