Context

Teams often use SQL as a first pass to validate raw data before reporting, modeling, or downstream processing. Interviewers ask this to see whether you can identify common data quality issues with simple, reliable queries.

Core Question

Explain how you would perform basic database validation using SQL. Your answer should cover:

1. How to validate row counts and overall completeness
2. How to check for NULL values in important columns
3. How to detect duplicate records or duplicate business keys
4. How to validate allowed values, ranges, or simple business rules
5. How to summarize findings clearly for stakeholders or engineers

Scope Guidance

Keep the discussion practical and focused on easy SQL techniques. The interviewer is not looking for a full data quality framework; they want to hear how you would use straightforward SELECT, WHERE, GROUP BY, and aggregate queries to catch common issues quickly.