Handling Nulls in Analytics Prep | Dataford Interview Questions

Your question is Handling Nulls in Analytics Prep. Take a moment with it on the right.

Talk me through your thinking if you like. When you're confident, submit your answer and I'll grade it like a real screen (7/10 or better passes).

Problem

Context

Analytics datasets often contain missing values, blank strings, duplicate records, and inconsistent categories. If these issues are not handled carefully, reports and downstream metrics become unreliable.

Question

Explain how you would handle NULL values and dirty data when preparing a dataset for analytics in SQL. Your answer should cover:

How to distinguish true NULLs from other dirty values such as empty strings, placeholder text, or invalid numbers
When to use filtering versus standardization versus default replacement
How functions like COALESCE, NULLIF, CASE WHEN, and aggregates behave with missing data
How your cleaning choices can affect business metrics such as counts, averages, and conversion rates

Scope Guidance

Keep the discussion practical and SQL-focused. The interviewer expects you to explain both the reasoning and the trade-offs, not just list functions. Use short PostgreSQL examples where helpful.

Your question is Handling Nulls in Analytics Prep. Take a moment with it on the right.

Talk me through your thinking if you like. When you're confident, submit your answer and I'll grade it like a real screen (7/10 or better passes).

Context

Question

Explain how you would handle NULL values and dirty data when preparing a dataset for analytics in SQL. Your answer should cover:

How to distinguish true NULLs from other dirty values such as empty strings, placeholder text, or invalid numbers
When to use filtering versus standardization versus default replacement
How functions like COALESCE, NULLIF, CASE WHEN, and aggregates behave with missing data
How your cleaning choices can affect business metrics such as counts, averages, and conversion rates

Scope Guidance

Keep the discussion practical and SQL-focused. The interviewer expects you to explain both the reasoning and the trade-offs, not just list functions. Use short PostgreSQL examples where helpful.