Database Engineer interview questions (53)

49 questions

• What are primary and foreign keys?

  Fresher
• What is the difference between DELETE, TRUNCATE and DROP?

  Fresher
• How does SQL treat NULL and how do you compare against it?

  Fresher
• Write a query that counts orders per customer

  Fresher
• What is the difference between UNION and UNION ALL?

  Fresher
• What is the difference between WHERE and HAVING?

  Fresher
• Which constraints can a column have in SQL?

  Fresher
• In what order does a SELECT query logically execute?

  Fresher
• Explain INNER, LEFT and FULL OUTER JOIN

  Junior
• Explain ACID with a bank transfer example

  Junior
• Write a query that returns the second highest salary

  Junior
• What is a CTE and how does it differ from a subquery?

  Junior
• Why does WHERE YEAR(created_at) = 2026 not use the index?

  Junior
• Write a query that finds and removes duplicate rows

  Junior
• How do you write an upsert in SQL?

  Junior
• Which columns should you index and which should you not?

  Junior
• What is the difference between COUNT(*), COUNT(column) and COUNT(DISTINCT column)?

  Junior
• Why can NOT IN return no rows, and what should you use instead?

  Junior
• Write a query that lists each employee with their manager's name

  Junior
• Your SUM doubled after you added a JOIN. What went wrong?

  Junior