10 Booz Allen SQL Interview Questions (Updated 2024)
Booz Allen employees write SQL queries to extract customer behavior patterns from their marketing databases and transform sales data into actionable insights for business growth, as well as to merge client information from different sources for personalized services. That is the reason why Booz Allen often ask SQL query questions in interviews for Data Science and Data Engineering positions.
Thus, to help you practice, here's 10 Booz Allen Hamilton SQL interview questions – can you solve them?
10 Booz Allen Hamilton SQL Interview Questions
SQL Question 1: Calculate Monthly Average Stars for Each Product
Booz Allen is interested in understanding the month to month feedback of their clients' products. You are given a dataset containing product reviews submitted by users. Each review includes a review id, the id of the user who submitted it, the submission date, the product id, and the star rating given to the product (from 1 to 5).
Write a SQL query to calculate the monthly average star rating for each product. Round up to two decimal places.
Example Input:
| review_id | user_id | submit_date | product_id | stars |
|---|---|---|---|---|
| 6171 | 123 | 06/08/2022 | 50001 | 4 |
| 7802 | 265 | 06/10/2022 | 69852 | 4 |
| 5293 | 362 | 06/18/2022 | 50001 | 3 |
| 6352 | 192 | 07/26/2022 | 69852 | 3 |
| 4517 | 981 | 07/05/2022 | 69852 | 2 |
Example Output:
| month | product_id | avg_stars |
|---|---|---|
| 6 | 50001 | 3.50 |
| 6 | 69852 | 4.00 |
| 7 | 69852 | 2.50 |
Answer:
In this solution, we're using the PostgreSQL function to isolate the month from the , and then we're grouping by both the month and product_id to find the average star rating for each combination. We are also using the function to round our average to two decimal points.
To solve a similar window function question on DataLemur's free interactive coding environment, try this Google SQL Interview Question:
SQL Question 2: Highly-Paid Employees
Given a table of Booz Allen employee salary data, write a SQL query to find all employees who earn more money than their direct boss.
Booz Allen Example Input:
| employee_id | name | salary | department_id | manager_id |
|---|---|---|---|---|
| 1 | Emma Thompson | 3800 | 1 | |
| 2 | Daniel Rodriguez | 2230 | 1 | 10 |
| 3 | Olivia Smith | 8000 | 1 | 8 |
| 4 | Noah Johnson | 6800 | 2 | 8 |
| 5 | Sophia Martinez | 1750 | 1 | 10 |
| 8 | William Davis | 7000 | 2 | NULL |
| 10 | James Anderson | 4000 | 1 | NULL |
Example Output:
| employee_id | employee_name |
|---|---|
| 3 | Olivia Smith |
This is the output because Olivia Smith earns $8,000, surpassing her manager, William Davis who earns 7,800.
Code your solution to this interview question directly within the browser on DataLemur:
Answer:
First, we perform a SELF-JOIN where we treat the first table () as the managers' table and the second table () as the employees' table. Then we use a clause to filter the results, ensuring we only get employees whose salaries are higher than their manager's salary.
If the code above is tough, you can find a detailed solution here: Well Paid Employees.
SQL Question 3: What is the difference between a primary key and a foreign key?
A primary key is a column (or set of columns) in a table that uniquely identifies each row in the table. It cannot contain null values and must be unique across all rows in the table.
A foreign key is a column (or set of columns) in a table that references the primary key of another table. It is used to establish a relationship between the two tables. A foreign key can contain null values, and multiple rows in the referencing table can reference the same row in the referenced table.
For example, consider a database with two tables: and . The Booz Allen customers table might have a primary key column called , while the Booz Allen orders table might have a foreign key column called that references the column in the table. This establishes a relationship between the two tables, such that each row in the orders table corresponds to a specific Booz Allen customer.
SQL Question 4: Project Resource Allocation and Utilisation
Booz Allen routinely carries out several consulting projects for its clients. The company typically assigns multiple consultants and other resources to these projects, often simultaneously. For any project, the Project Manager would like to know how many and which consultants are assigned to their project and when. They would also like to understand the allocation and utilisation pattern of their project consultants by tracking their respective working hours.
Example Input:
| id | name | start_date | end_date |
|---|---|---|---|
| 1001 | Project Alpha | 2022-06-01 | 2022-09-30 |
| 1002 | Project Beta | 2022-07-01 | 2022-11-30 |
| 1003 | Project Gamma | 2022-06-20 | 2022-08-31 |
Example Input:
| id | name |
|---|---|
| 501 | John Doe |
| 502 | Jane Doe |
| 503 | Richard Roe |
Example Input:
| project_id | consultant_id | start_date | end_date | hours_per_week |
|---|---|---|---|---|
| 1001 | 501 | 2022-06-01 | 2022-09-30 | 30 |
| 1001 | 502 | 2022-06-15 | 2022-08-15 | 20 |
| 1002 | 502 | 2022-07-15 | 2022-11-15 | 30 |
| 1002 | 503 | 2022-07-01 | 2022-09-30 | 25 |
| 1003 | 501 | 2022-06-20 | 2022-07-31 | 40 |
| 1003 | 503 | 2022-06-30 | 2022-08-20 | 20 |
Write a SQL query to fetch the list of consultants and their respective weekly hours allocated to Project Alpha.
Answer:
This query joins the project_allocations and consultants tables to fetch the consultant names and their respective hours_per_week. It filters the result set to include the rows associated with 'Project Alpha' by utilising a subquery.
SQL Question 5: What do the / operators do, and can you give an example?
The / operator is used to remove to return all rows from the first SELECT statement that are not returned by the second SELECT statement.
Note that is available in PostgreSQL and SQL Server, while MINUS is available in MySQL and Oracle (but don't stress about knowing which DBMS supports what exact commands since the interviewers at Booz Allen should be lenient!).
For a tangible example in PostgreSQL, suppose you were doing an HR Analytics project for Booz Allen, and had access to Booz Allen's contractors and employees data. Assume that some employees were previously contractors, and vice versa, and thus would show up in both tables. You could use operator to find all contractors who never were a employee using this query:
SQL Question 6: Filter Customer Records Based on Multiple Conditions.
Assume Booz Allen has a client in the telecommunications industry and is maintaining a database of the client's customers. You have been asked to retrieve the records of customers who are from 'Virginia' and 'California', are on 'Plan B' or 'Plan C', and have not made a payment in the last 6 months.
Example Input:
| customer_id | state | plan | last_payment_date |
|---|---|---|---|
| 1782 | Virginia | Plan A | 05/01/2022 |
| 4536 | California | Plan B | 11/18/2021 |
| 8374 | Virginia | Plan B | 12/23/2021 |
| 5123 | Nevada | Plan C | 01/15/2022 |
| 1298 | California | Plan C | 07/05/2022 |
Answer:
In this question, we're using PostgreSQL's , , , and functions to filter customer records within the criteria provided by the client. After running this SQL query, you should get the list of customers who belong to 'Virginia' or 'California', are on 'Plan B' or 'Plan C', and have not made a payment in the last six months.
SQL Question 7: What would you do to speed up a slow SQL query?
Here's some strategies that can generally speed up a slow SQL query:
- Only query the columns you actually need
- Index the columns used in the query
- Use the right kind of JOIN (be explicit about inner vs. outer joins)
- Use the right data types (for example INT vs BIGINT can save you disk space and memory)
While there's an entire industry dedicated to database performance tuning , for Data Analyst and Data Science interviews at Booz Allen, knowing the above basics should be more than enough to ace the SQL interview! Data Engineers on the other hand should know more about the command and understand a bit more about a query-execution plan.
SQL Question 8: Find the average working hours of employees in a department
For a company like Booz Allen, a leading management consulting firm, it is important to measure the average number of hours worked by employees in a specific department. This can help determine if there's an uneven distribution of workload or if some departments have longer working hours compared to others.
Imagine we have two tables: and .
Example Input:
| employee_id | first_name | last_name | department_id |
|---|---|---|---|
| 001 | John | Doe | 100 |
| 002 | Jane | Smith | 200 |
| 003 | Bob | Johnson | 100 |
| 004 | Monica | Geller | 200 |
| 005 | Chandler | Bing | 300 |
Example Input:
| employee_id | hours_worked |
|---|---|
| 001 | 8 |
| 002 | 9 |
| 003 | 9 |
| 004 | 8 |
| 005 | 8 |
The task is to find the average hours worked in each department. So the output should be:
Example Output:
| department_id | avg_hours_worked |
|---|---|
| 100 | 8.5 |
| 200 | 8.5 |
| 300 | 8.0 |
Answer:
You can solve this problem with a combination of JOIN, GROUP BY and AVG functions in PostgreSQL:
In above query, we join two tables using employee ids and group by department ids to calculate average hours worked in each department. The AVG function then calculates the average of these grouped hours. The result is a list of departments with their corresponding average hours worked. It helps in analyzing the workload distribution across different departments.
To practice a very similar question try this interactive Amazon Server Utilization Time Question which is similar for aggregating company data for analysis or this Microsoft Teams Power Users Question which is similar for analysing data across multiple workers.
SQL Question 9: Click-Through Rate Calculation for Booz Allen
Booz Allen, a leading strategy and technology consulting firm, is running an online advertising campaign with different ads. They track impressions and clicks to analyze the campaign's performance. To better understand their data, they'd like you to calculate the 'Click-Through-Rate' (CTR). CTR is defined as the total number of clicks an ad receives divided by the total number of impressions (each ad display counts as one impression), multiplied by 100 (%).
Assuming you are provided with two tables: and .
Example Input:
| ad_id | timestamp | user_id |
|---|---|---|
| 1 | 06/08/2022 00:00:00 | 20 |
| 2 | 06/10/2022 00:00:00 | 30 |
| 1 | 06/11/2022 00:00:00 | 40 |
| 3 | 07/26/2022 00:00:00 | 50 |
| 2 | 07/05/2022 00:00:00 | 60 |
Example Input:
| ad_id | timestamp | user_id |
|---|---|---|
| 1 | 06/08/2022 00:00:00 | 10 |
| 1 | 06/08/2022 00:00:00 | 20 |
| 2 | 06/10/2022 00:00:00 | 70 |
| 3 | 07/26/2022 00:00:00 | 80 |
| 2 | 07/05/2022 01:00:00 | 60 |
| 1 | 07/05/2022 02:00:00 | 90 |
Answer:
This query calculates the CTR by calculating the ratio of total clicks to total impressions for each ad and then multiplying it by 100 to give a percentage. The joins in the subqueries are to aggregate the counts on ad_id for both clicks and impressions. The result is served for each ad_id.
To solve a related problem on DataLemur's free online SQL coding environment, try this SQL interview question asked by Facebook:
SQL Question 10: Do and a typically produce equivalent results?
For all practical purposes, and do NOT produce the same results.
While both are similar in that they combine two tables, you can think of joins as increasing the width of the resulting table (you'll have more columns in the result set for a left/inner/right join), whereas a union is used to combine rows which increases the height of the result set but keeps the column count the same.
If your familiar with set operations, you can think of a as set addition, whereas a is set multiplication.
How To Prepare for the Booz Allen SQL Interview
The best way to prepare for a SQL interview, besides making sure you have strong SQL fundamentals, is to practice a ton of real SQL questions that were asked in recent job interviews. In addition to solving the above Booz Allen SQL interview questions, you should also solve the 200+ DataLemur SQL Interview Questions which come from companies like Google, Microsoft and Silicon Valley startups.
Each SQL question has multiple hints, full answers and most importantly, there's an online SQL code editor so you can instantly run your query and have it executed.
To prep for the Booz Allen SQL interview you can also be helpful to solve SQL problems from other consulting and professional service companies like:
Discover how Booz Allen is leveraging Artificial Intelligence to solve complex problems and transform industries!
However, if your SQL foundations are weak, don't worry about going right into solving questions – go learn SQL with this SQL interview tutorial.
This tutorial covers things like functions like SUM()/COUNT()/AVG() and ordering data – both of these come up often in Booz Allen SQL interviews.
Booz Allen Hamilton Data Science Interview Tips
What Do Booz Allen Data Science Interviews Cover?
Besides SQL interview questions, the other topics tested in the Booz Allen Data Science Interview are:
- Statistics and Probability Questions
- Python Pandas or R Coding Questions
- Product Analytics Questions
- ML Modelling Questions
- Behavioral & Resume-Based Questions
How To Prepare for Booz Allen Data Science Interviews?
I think the best way to prep for Booz Allen Data Science interviews is to read the book I wrote: Ace the Data Science Interview.
It solves 201 data interview questions taken from companies like Google, Tesla, & Goldman Sachs. The book's also got a crash course covering Product Analytics, SQL & ML. And finally it's vouched for by the data community, which is how it's gotten to be an Amazon best-seller with over 1000+ 5-star reviews.
While the book is more technical, it's also crucial to prepare for the Booz Allen behavioral interview. A good place to start is by understanding the company's cultural values.