SQL for Database Validation

Context

Database validation is a common part of analytics engineering, ETL testing, and production data quality checks. Interviewers ask this to understand whether you can use SQL to confirm that data is complete, accurate, and consistent.

Core Question

Describe your experience using SQL for database validation. In your answer, explain how you would use SQL to:

1. Check row counts and record completeness
2. Detect nulls, duplicates, and invalid values
3. Validate aggregates and business rules
4. Compare source and target datasets after a load

Scope Guidance

Keep the discussion practical rather than theoretical. The interviewer expects a structured explanation of the most common validation patterns, the SQL queries you would write, what issues they catch, and how you would prioritize checks in a real workflow.