Optimize Slow Database Query

Explain how you would optimize a slow-running database query that handles millions of customer records at PayJoy.

For the practical portion, provide a PostgreSQL query that returns active customers with active loans, a positive outstanding balance, and no successful latest payment. Assume the query must remain correct at large scale.

Output

1. One row per qualifying loan, with customer_id, full_name, loan_id, outstanding_balance, latest_payment_date, and latest_payment_status
2. Include only active customers and loans with a positive balance whose latest payment is missing or not successful
3. Order by outstanding_balance descending, then customer_id ascending