8 Bain & Company SQL Interview Questions (Updated 2024)
At Bain & Company, SQL is essential for analyzing business performance metrics like revenue growth, customer acquisition costs, and sales conversion rates. These insights are used to create detailed client reports that highlight areas for improvement and identify growth opportunities, which is why Bain & Company frequently includes SQL problems in interviews for Data Science, Analytics, and Data Engineering jobs.
So, to help you practice, we've curated 8 Bain Consulting SQL interview questions – how many can you solve?
8 Bain Consulting SQL Interview Questions
SQL Interview Question 1: Identifying Power Users for Bain & Company
As a member of Bain & Company, you are required to constantly monitor and recognize key clients who provide significant business value. Power users of Bain & Company are identified as the clients who have frequently used Bain's consulting services in the last six months. Please write a PostgreSQL query to find all users who have used Bain's services more than ten times in the last six months.
Consider the following tables:
Example Input
| client_id | client_name |
|---|---|
| 1 | Microsoft Corporation |
| 2 | Apple Inc. |
| 3 | Amazon.com, Inc. |
| 4 | Google LLC |
Example Input:
| consultation_id | client_id | consultation_date | service_id |
|---|---|---|---|
| 1 | 1 | 6/10/2022 | 100 |
| 2 | 1 | 6/15/2022 | 101 |
| 3 | 2 | 6/20/2022 | 102 |
| 4 | 2 | 6/25/2022 | 101 |
| 5 | 1 | 6/30/2022 | 100 |
| 6 | 3 | 7/5/2022 | 103 |
| 7 | 1 | 7/10/2022 | 100 |
| 8 | 4 | 7/15/2022 | 100 |
| 9 | 1 | 7/20/2022 | 101 |
| 10 | 1 | 7/25/2022 | 102 |
| 11 | 2 | 7/30/2022 | 101 |
| 12 | 1 | 8/4/2022 | 100 |
Answer:
In PostgreSQL, you can use a subquery to count the clients who had more than 10 consultations within the last six months, and then filter these clients. Here is the query.
This query first joins with on the field, filters for entries within the last six months, and then counts the number of consultations per client. The outer query then filters for the clients with more than 10 consultations. Please replace the to contain the last six months from your specific required date. The result will include the and of all power users.
To practice another SQL customer analytics question where you can solve it right in the browser and have your SQL code instantly executed, try this Walmart SQL Interview Question:
SQL Question 2: Top 3 Salaries
Imagine there was a table of Bain & Company employee salary data. Write a SQL query to find the top 3 highest earning employees within each department.
Bain & Company Example Input:
| employee_id | name | salary | department_id |
|---|---|---|---|
| 1 | Emma Thompson | 3800 | 1 |
| 2 | Daniel Rodriguez | 2230 | 1 |
| 3 | Olivia Smith | 2000 | 1 |
| 4 | Noah Johnson | 6800 | 2 |
| 5 | Sophia Martinez | 1750 | 1 |
| 8 | William Davis | 6800 | 2 |
| 10 | James Anderson | 4000 | 1 |
Example Input:
| department_id | department_name |
|---|---|
| 1 | Data Analytics |
| 2 | Data Science |
Example Output:
| department_name | name | salary |
|---|---|---|
| Data Analytics | James Anderson | 4000 |
| Data Analytics | Emma Thompson | 3800 |
| Data Analytics | Daniel Rodriguez | 2230 |
| Data Science | Noah Johnson | 6800 |
| Data Science | William Davis | 6800 |
Test your SQL query for this problem directly within the browser on DataLemur:
Answer:
We use the DENSE_RANK() window function to generate unique ranks for each employee's salary within their department, with higher salaries receiving lower ranks. Then, we wrap this up in a CTE and filter the employees with a ranking of 3 or lower.
If the code above is tough, you can find a step-by-step solution here: Top 3 Department Salaries.
SQL Question 3: Can you describe the concept of a database index and the various types of indexes?
A database index is a way to optimize the performance of a database by reducing the amount of data that needs to be searched to retrieve a record.
There are several types of indexes:
- unique & non-unuqie indexes
- primary & composite indexes
- clustered & non-clustered indexes
SQL Question 4: Analyze Sales Performance with Window Function
As a data analyst at Bain & Company, you're tasked to analyze the sales data of various products sold over some period. Each product is sold by a certain seller and has its respective sales quantity and date of sales. You're required to write a SQL query to:
- Calculate the total sales of each seller in each month.
- Determine each seller's month-over-month percentage change in total sales.
You can assume that there's always at least one product sold by a seller in a month. To calculate the month-over-month growth rate, you should use the following formula:
(THIS_MONTH_SALES - LAST_MONTH_SALES) / LAST_MONTH_SALES * 100.0
The output should be sorted by seller's ID then by sales month in ascending order.
Here is a sample data of products sold:
Example Input:
| sale_id | seller_id | sale_date | product_id | quantity |
|---|---|---|---|---|
| 201 | 1 | 01/05/2021 | A | 100 |
| 202 | 2 | 01/12/2021 | B | 80 |
| 203 | 1 | 02/15/2021 | A | 120 |
| 204 | 2 | 02/20/2021 | B | 90 |
| 205 | 1 | 03/10/2021 | A | 150 |
| 206 | 2 | 03/25/2021 | B | 100 |
Example Output:
| seller | month | total_sales | mom_growth |
|---|---|---|---|
| 1 | 5 | 100 | null |
| 1 | 6 | 120 | 20.0 |
| 1 | 7 | 150 | 25.0 |
| 2 | 5 | 80 | null |
| 2 | 6 | 90 | 12.5 |
| 2 | 7 | 100 | 11.1 |
Answer:
The above query first squashes the sales table into a monthly_sales view that aggregates the monthly sales for each seller. Then, the LAG window function is introduced to get the sales of the previous month. Finally, the month-over-month growth rate is calculated and null values are replaced with 0 (where applicable) to avoid division by zero issues.
To practice a related window function SQL problem on DataLemur's free interactive SQL code editor, solve this Google SQL Interview Question:
SQL Question 5: Can you explain the difference between a foreign and primary key in a database?
To better understand the difference between a primary key and a foreign key, let's use an example from Bain & Company's marketing analytics database, which holds data on Google Ads campaigns:
:
| ad_id | campaign_id | keyword | click_count |
|---|---|---|---|
| 1 | 100 | Bain & Company pricing | 10 |
| 2 | 100 | Bain & Company reviews | 15 |
| 3 | 101 | Bain & Company alternatives | 7 |
| 4 | 101 | buy Bain & Company | 12 |
In this table, serves as the primary key. It uniquely identifies each ad and cannot be null.
is a foreign key that connects to the of the corresponding Google Ads campaign. This establishes a relationship between the ads and their campaigns, enabling easy querying to find which ads belong to a specific campaign or which campaigns a specific ad belongs to.
The table may also have multiple foreign keys that reference primary keys in other tables. For example, and foreign keys could be used to link each ad to its ad group and the Google Ads account that the campaigns belong to, respectively.
SQL Question 6: Filter Customers Based on Subscription and Region
As a data analyst in Bain & Company, you are asked to find all the customers who have an 'active' subscription and belong to 'region A' from their recent subscription data. Can you write an SQL query to get this data?
Here is a snapshot of the 'customers' table for your reference:
Example Input:
| customer_id | customer_name | subscription_status | region |
|---|---|---|---|
| 101 | James | Active | A |
| 102 | Linda | Inactive | B |
| 103 | Michael | Active | C |
| 104 | Sarah | Active | A |
| 105 | John | Inactive | A |
| 106 | Angela | Active | A |
| 107 | David | Active | B |
The output should give the Customer ID and Customer Name of customers who have 'active' subscription and belong to 'region A'.
Example Output:
| customer_id | customer_name |
|---|---|
| 101 | James |
| 104 | Sarah |
| 106 | Angela |
Answer:
The SQL query to obtain the data would be:
This query selects data from the table where the is 'Active' and is 'A'. The WHERE clause is used to filter rows using the conditions provided, and the AND operator is used to ensure all conditions are satisfied by the filtered results.
SQL Question 7: What does the operator do?
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 worry about knowing which DBMS supports which exact commands since Bain & Company interviewers aren't trying to trip you up on memorizing SQL syntax).
For a tangible example of in PostgreSQL, suppose you were doing an HR Analytics project for Bain & Company, and had access to Bain & Company'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 8: Average Monthly Revenue from Different Service Sectors
Bain & Company provides services across diverse sectors to different clients. The management would like to track their monthly performance in terms of revenue across various sectors. They have information on the revenue generated by each transaction. Could you write a SQL query to find the average monthly revenue generated from each service sector? The results should be ordered by the average revenue in descending order.
Example Input:
| transaction_id | transaction_date | service_sector | client_id | revenue |
|---|---|---|---|---|
| 8976 | 05/07/2021 00:00:00 | Technology | 9258 | $10,000 |
| 6723 | 07/14/2021 00:00:00 | Energy | 6412 | $20,000 |
| 3258 | 05/02/2021 00:00:00 | Technology | 5213 | $15,000 |
| 7121 | 07/22/2021 00:00:00 | Retail | 3147 | $25,000 |
| 9135 | 06/15/2021 00:00:00 | Energy | 8365 | $50,000 |
Example Output:
| month | service_sector | avg_revenue |
|---|---|---|
| 07 | Energy | $20,000 |
| 07 | Retail | $25,000 |
| 06 | Energy | $50,000 |
| 05 | Technology | $12,500 |
Answer:
This query first extracts the month from the transaction_date field and groups the data by this month and the service sector. The AVG function is used to calculate the average revenue for each combination of month and service sector, and the results are sorted in descending order of average revenue.
How To Prepare for the Bain & Company 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. Beyond just solving the above Bain & Company SQL interview questions, you should also solve the 200+ DataLemur SQL Interview Questions which come from companies like Microsoft, Google, and Meta.
Each interview question has multiple hints, detailed solutions and crucially, there's an online SQL code editor so you can easily right in the browser your SQL query and have it graded.
To prep for the Bain & Company SQL interview you can also be wise to solve SQL questions from other management consulting companies like:
Discover how Bain & Company’s data and analytics transformation strategies are helping companies thrive in the digital era!
However, if your SQL foundations are weak, forget about jumping right into solving questions – strengthen your SQL foundations with this interactive SQL tutorial.
This tutorial covers SQL topics like LEAD window function and finding NULLs – both of which pop up frequently during Bain & Company interviews.
Bain Consulting Data Science Interview Tips
What Do Bain & Company Data Science Interviews Cover?
In addition to SQL interview questions, the other types of questions covered in the Bain & Company Data Science Interview include:
- Probability & Statistics Questions
- Coding Questions in Python or R
- Business Sense and Product-Sense Questions
- Machine Learning Questions
- Behavioral Interview Questions based on Bain & Company cultural values
How To Prepare for Bain & Company Data Science Interviews?
To prepare for Bain & Company Data Science interviews read the book Ace the Data Science Interview because it's got:
- 201 interview questions sourced from Facebook, Google & startups
- a refresher covering SQL, AB Testing & ML
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Also focus on the behavioral interview – prep for that using this list of common Data Scientist behavioral interview questions.