SQL Interview Questions

Complimentary to the blog post on Qindi (Cindy) Zhang

SQL interview question bank:

On candidate’s basic understanding on data structure and SQL fundamentals:

  1. Can you interchange where and having clause?
  2. What is a correlated sub-query?

On candidate’s actual hands on SQL experience:

  1. How to perform unpivot in SQL?
  2. How large is the dataset you typically query against? What are some of the things you do to improve query efficiency?

On candidate’s business exposure and understanding:

  1. What is a business case where you need to use full join?
  2. How do you handle missing days in a transaction report if dashboard users want this information captured and reflected?

For the technical interview, it’s best to combine some actually code writing with conceptual questions  such as above. That way you as an interviewer can evaluate how familiar the candidate is with the basics, how comfortable she is at writing code, how much of her knowledge is from book vs. from practice. And furthermore, how well the analyst is able to grasp the underlying business requirement and deliver the analytics product that satisfies stakeholder’s need.
Interviewers, I hope this gives you an easy start!