Walk through your approach to debugging and optimizing a sluggish SQL query handling millions of records.
Use the provided PostgreSQL schema to write an efficient equivalent query that reports paid invoice revenue for January and February 2025. Explain how you would inspect the execution plan, identify bottlenecks, and choose indexes.
Output
- One row per billing month and customer segment.
- Columns:
billing_month, segment, invoice_count, and total_revenue.
- Include only paid invoices in the specified date range, include zero-value invoices with line items, sort by month and segment, and place a null segment last.
