You are given raw customer feedback records from an Orange survey export. Write a PostgreSQL query that returns the number of valid feedback submissions by channel, excluding rows with missing customer_id, blank feedback_text, or non-positive rating. Sort the result by the count descending, then by channel ascending.
| Column | Type | Description |
|---|---|---|
| feedback_idPK | INT | Unique feedback record identifier |
| customer_id | INT | Customer identifier; may be NULL in invalid records |
| channel | VARCHAR(50) | Feedback source channel |
| feedback_text | TEXT | Free-text feedback message |
| rating | INT | Rating from 1 to 5; invalid rows may contain 0 or negative values |
| submitted_at | DATE | Date the feedback was submitted |