Conquer Amazon SQL Interview Questions: Your Ultimate Prep Guide

Are you gearing up for an SQL interview at Amazon? Brace yourself, because the SQL rounds are notorious for their difficulty, especially for roles like Data Analyst, Data Scientist, Data Engineer, and Business Intelligence Engineer (BIE). But fear not! We’ve got your back with this comprehensive guide, packed with real Amazon SQL interview questions and expert tips to help you ace the interview and secure your dream job at one of the world’s tech giants.

Understanding Amazon’s Interview Process

Before we dive into the SQL questions, let’s briefly discuss Amazon’s interview process. Known for its rigorous and challenging nature, the company follows a structured approach that typically includes multiple rounds. For data-centric roles, you can expect SQL assessments, coding challenges, behavioral interviews, and case studies.

Amazon places a strong emphasis on its leadership principles, such as customer obsession, ownership, insisting on the highest standards, and bias for action. Throughout the interview process, you’ll be evaluated not only on your technical skills but also on how well you align with these principles.

Real Amazon SQL Interview Questions

Now, let’s dive into the real SQL interview questions that have been asked in recent Amazon interviews. We’ve curated a diverse set of questions to help you prepare for various scenarios and challenges.

1. Average Review Ratings

In a recent Amazon data analyst interview, the candidate was given the reviews table and asked to write a SQL query to get the average star ratings for each product, every month. The output should include the month in numerical value, product ID, and the average star rating rounded to two decimal places, sorted by month and then by product ID.

-- Example Input:review_id | user_id | submit_date            | product_id | stars----------+---------+-------------------------+------------+-------     61711|    23062| 2022-06-08 00:00:00    |      50001 |     4     78022|    65062| 2022-06-10 00:00:00    |      69852 |     3     52933|    62062| 2022-06-18 00:00:00    |      50001 |     5     63521|    92072| 2022-07-26 00:00:00    |      69852 |     2     51798|    10752| 2022-07-05 00:00:00    |      69852 |     5-- Example Output:mth | product | avg_stars-----+----------+----------   6 |    50001 |     3.50   6 |    69852 |     4.00   7 |    69852 |     2.50

To solve this problem, you’ll need to use the EXTRACT function to retrieve the month from the submit_date column and then calculate the average star rating per product and month, rounded to two decimal places.

2. SQL Query Optimization

During the interview, you might be asked about optimizing slow SQL queries. This question tests your understanding of database performance and best practices. Here are some potential optimization techniques you should be familiar with:

• Selecting specific fields instead of using SELECT *
• Avoiding SELECT DISTINCT when unnecessary
• Creating joins with INNER JOIN instead of using WHERE clauses
• Reducing the number of joins when possible (consider denormalization)
• Adding indexes to frequently queried columns
• Examining the SQL query execution plan

Be prepared to provide examples or real-life scenarios where you’ve optimized SQL queries for better performance.

3. SQL Constraints

You might be asked about SQL constraints and their different types. SQL constraints are rules that enforce data integrity within a database table. Some common constraints include:

• NOT NULL: Prevents null values from being inserted into a column
• UNIQUE: Ensures that all values in a column are unique
• INDEX: Speeds up queries by creating an index on a specific column
• PRIMARY KEY: Uniquely identifies each record in a table
• FOREIGN KEY: Enforces referential integrity between tables

Be ready to explain these constraints and provide examples of when you might use them.

4. Highest-Grossing Items

Assume you’re given a table containing information about Amazon customers and their spending on products in various categories. The interviewer might ask you to identify the top two highest-grossing products within each category in a specific year, such as 2022. The expected output should include the category, product, and total spend.

-- Example Input:category   | product        | user_id | spend | transaction_date------------+----------------+---------+-------+------------------appliance   | refrigerator   |     165 |  46.00| 2021-12-26 12:00:00appliance   | refrigerator   |     123 | 299.99| 2022-03-02 12:00:00appliance   | washing machine|     123 | 219.80| 2022-03-02 12:00:00electronics | vacuum         |     178 | 152.00| 2022-04-05 12:00:00electronics | wireless headset|    156 | 249.90| 2022-07-08 12:00:00electronics | vacuum         |     145 | 189.00| 2022-07-15 12:00:00-- Example Output:category   | product        | total_spend------------+----------------+-------------appliance   | refrigerator   |      299.99appliance   | washing machine|      219.80electronics | vacuum         |      341.00electronics | wireless headset|      249.90

To solve this problem, you’ll need to group the data by category and product, calculate the total spend for each combination, filter for transactions in 2022, and then use the RANK or DENSE_RANK function to identify the top two highest-grossing products within each category.

5. Difference Between RANK and DENSE_RANK

Speaking of ranking functions, you might be asked to explain the difference between RANK and DENSE_RANK. Both functions are used to assign ranks to rows within a partition, but they handle ties differently.

• RANK: Assigns the same rank to tied rows, but then skips the next rank(s) based on the number of tied rows.
• DENSE_RANK: Assigns the same rank to tied rows, but the next rank follows consecutively, without skipping any ranks.

Be prepared to provide examples that illustrate the differences between these two ranking functions.

6. Amazon Orders SQL Assessment

In some interviews, you might be given a multi-part SQL assessment based on Amazon’s order data. Here’s an example of the tables and questions you might encounter:

Tables:

• ORDERS (order_id, customer_id, order_datetime, item_id, order_quantity)
• ITEMS (item_id, item_category)

Questions:

1. How many units were ordered yesterday?
2. In the last 7 days (including today), how many units were ordered in each category? (Consider all categories, even those with zero orders.)
3. Write a query to get the earliest order_datetime for all customers for each date they placed an order. (Customers can place multiple orders on a single day.)
4. Write a query to find the second earliest order_datetime for each customer for each date they placed two or more orders.

These types of multi-part SQL assessments test your ability to write complex queries, understand database relationships, and handle different scenarios.

Interview Preparation Tips

Preparing for Amazon SQL interviews requires dedication and practice. Here are some tips to help you along the way:

• Practice, practice, practice: Solve as many SQL interview questions as possible, including those from Amazon and other tech companies. Platforms like DataLemur and LeetCode offer a wide range of SQL problems to practice.
• Learn SQL fundamentals: Make sure you have a solid understanding of SQL concepts, including joins, subqueries, window functions, and aggregate functions.
• Understand database design: Familiarize yourself with database normalization, indexing, and query optimization techniques.
• Study Amazon’s leadership principles: Research and internalize Amazon’s leadership principles, as they will be evaluated during behavioral and case study interviews.
• Conduct mock interviews: Practice mock interviews with friends or online resources to improve your communication skills and gain confidence.
• Stay up-to-date: Follow industry blogs, forums, and online communities to stay informed about the latest trends and techniques in data analysis and engineering.

Conclusion

Preparing for Amazon SQL interviews can be a daunting task, but with the right approach and dedication, you can increase your chances of success. By practicing real Amazon SQL interview questions, understanding the company’s interview process, and following our expert tips, you’ll be well-equipped to showcase your skills and impress the interviewers.

Remember, the SQL rounds are just one part of the Amazon interview process. Don’t forget to prepare for other aspects, such as coding challenges, behavioral interviews, and case studies. With perseverance and a growth mindset, you can conquer the Amazon SQL interview and take the first step towards an exciting career at one of the world’s most innovative companies.

Good luck!