Handling Missing Demographic Data

Context

At companies like BrightCart, demographic fields such as age group, gender, and region are often used in reporting and segmentation. If 30% of critical demographic data is missing, analysts need a practical SQL-based approach that preserves data quality without introducing misleading assumptions.

Question

Explain how you would handle a dataset where 30% of the critical demographic data is missing. In your answer, discuss:

1. How you would measure and profile the missingness in SQL
2. When to exclude rows versus keep them with an Unknown category
3. How CASE WHEN, COALESCE, and basic aggregations can help with reporting
4. What risks missing demographic data creates for downstream analysis

Scope guidance

The interviewer expects a practical, SQL-oriented explanation rather than advanced statistical imputation. Focus on simple, defensible approaches that are appropriate for reporting and exploratory analysis in PostgreSQL.