Challenge: Error Handling

Refactor the provided query using the sales_data table to ensure it is robust, error-proof, and handles inconsistent data gracefully.

1. Implement fault-tolerant calculations to prevent runtime errors:
   • Use SAFE_DIVIDE for division operations to prevent division by zero;
   • Use COALESCE on the sales_price column to replace NULL values with 0;
   • Ensure your query returns safe calculated columns without failing.
2. Navigate arrays safely to avoid out-of-bounds errors:
   • Use SAFE_OFFSET to extract elements from arrays;
   • Ensure that missing indices return NULL instead of causing the query to crash.
3. Ensure structural integrity and add validation flags:
   • Handle LEFT JOIN nulls by replacing missing joined values with "Unknown";
   • Add a new column to flag potential data quality issues (e.g., missing data, negative price, invalid quantity);
   • Ensure your final query keeps data issues visible for debugging rather than silently filtering them out.