Rolling 30-Day Transaction Average

Write a query using SQL window functions to calculate a rolling 30-day average of transaction volumes per user.

Use the transactions table. Aggregate multiple transactions occurring for the same user on the same date before calculating the rolling average. Include dates whose transaction volume is NULL, following PostgreSQL aggregate behavior.

Output

1. One row per user and transaction date
2. Columns: user_id, transaction_date, daily_volume, and rolling_30_day_avg
3. Include the current date and the preceding 29 calendar days in each average
4. Order by user_id, then transaction_date ascending