Top SQL Interview Questions

Top SQL Interview Questions

Top SQL Interview Questions. A tutorial on common SQL questions and their answers. Here are a dozen of the most common SQL interview questions you will see during an interview for a data professional role.

Here are a dozen of the most common SQL interview questions you will see during an interview for a data professional role. I would highly suggest you attempt to answer the questions and write prospective queries for each question before you compare your answers to mine at the end of the article. To answer these questions, I created a fake dataset and a schema to run queries against. The database schema is outlined just below the questions. That will get you started. Once you finish the questions, you can scroll past the data tables to see the answers.

Questions

  1. Determine the number of duplicates in a table.
  2. Find all unique combinations of two columns.
  3. Count the number of non-null entries in a column.
  4. When to use group-by vs. distinct? Show an example.
  5. Why use coalesce vs. case statements?
  6. When would you choose left join over an inner join? Show an example.
  7. In what cases is a subquery a bad idea?
  8. Why is a temp table a good or bad idea?
  9. When are unions useful? Show an example.
  10. How to filter using a join? Show an example.
  11. When to use having vs. where? Show an example.
  12. How do common table expressions help an analyst? Show an example.

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