8 ResMed SQL Interview Questions (Updated 2024)
At ResMed, SQL is used to analyze patient sleep data, allowing them to develop better solutions for sleep disorders. They also rely on SQL to optimize the manufacturing process of respiratory medical equipment, ensuring high-quality products reach those in need, this is the rason why ResMed asks SQL questions during interviews for Data Science and Data Engineering positions.
To help you prep for the ResMed SQL interview, we've curated 8 ResMed SQL interview questions in this article.
8 ResMed SQL Interview Questions
SQL Question 1: Identify Top Customers for ResMed Based on Purchase Frequency
ResMed is a company that manufactures products for the diagnosis, treatment and management of sleep disorders, including sleep apnea, chronic obstructive pulmonary disease (COPD), and other respiratory conditions. ResMed uses a customer database, where crucial customer and transaction information is stored.
Your task is to write a query that identifies ResMed's highest value customers -- these are customers that buy ResMed products most frequently. More concretely, find customers who have placed the top 5 most orders. For simplicity, assume that each transaction record corresponds to one unique order.
Here is a sample data set:
Example Input:
| customer_id | first_name | last_name |
|---|---|---|
| 1001 | John | Doe |
| 1002 | Jane | Smith |
| 1003 | Alice | Johnson |
| 1004 | Bob | Williams |
| 1005 | Charlie | Brown |
Example Input:
| transaction_id | customer_id | transaction_date |
|---|---|---|
| 5682 | 1001 | 2022-01-01 |
| 6105 | 1002 | 2022-02-02 |
| 6134 | 1001 | 2022-03-03 |
| 6758 | 1003 | 2022-04-04 |
| 7189 | 1001 | 2022-05-05 |
| 7312 | 1003 | 2022-06-06 |
| 7894 | 1004 | 2022-07-07 |
| 8214 | 1003 | 2022-08-08 |
| 8463 | 1004 | 2022-09-09 |
| 8709 | 1005 | 2022-10-10 |
Answer:
This query groups the table by , and counts the numbers of (orders) for each customer. We then order the results by in descending order and pick the top 5. These will be the customers who have the highest number of orders. To link this result back to customer names or other customer details, you'd need to join this result set with the table on the field.
To practice another SQL customer analytics question where you can solve it right in the browser and have your SQL query instantly executed, try this Walmart SQL Interview Question:
Explore ResMed's latest innovations in digital health solutions aimed at improving sleep health and enhancing the therapy journey for sleep apnea patients! Understanding ResMed's advancements can provide valuable insights into how technology is transforming healthcare and patient engagement.
SQL Question 2: Top Department Salaries
Assume you had a table of ResMed employee salary data. Write a SQL query to find the top 3 highest paid employees within each department.
ResMed 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 |
Solve this question and run your code right in DataLemur's online SQL environment:
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 detailed solution here: Top 3 Department Salaries.
SQL Question 3: Can you explain what an index is 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-inuqie indexes
- primary & composite indexes
- clustered & non-clustered indexes
SQL Question 4: Identify Best Performing Product
As a part of your role at ResMed, which offers quality sleep, respiratory care, and digital health technology products, you're asked to evaluate the performance of various products based on customer reviews. Write a SQL query that given a table 'reviews', it returns the product with the highest average star rating.
Each row of contains:
- : The ID of the review
- : The ID of the user who submitted the review
- : The date when the review was submitted
- : The ID of the product being reviewed
- : The number of stars assigned by the user (on a scale from 1-5)
Example Input:
| review_id | user_id | submit_date | product_id | stars |
|---|---|---|---|---|
| 6171 | 123 | 2021-10-5 00:00:00 | 50001 | 4 |
| 7802 | 265 | 2022-10-5 00:00:00 | 69852 | 4 |
| 5293 | 362 | 2022-10-5 00:00:00 | 50001 | 3 |
| 6352 | 192 | 2021-11-5 00:00:00 | 69852 | 3 |
| 4517 | 981 | 2021-12-5 00:00:00 | 69852 | 2 |
Answer:
Given we want to compute average ratings per product, a window function isn't required. An aggregation would suffice.
The above query calculates the average star rating for each product (the part), and then orders the results in descending order of . The ensures that only the product with the highest average star rating is returned.
Pro Tip: Window functions are a frequent SQL interview topic, so practice all the window function problems on DataLemur
SQL Question 5: Can you explain the purpose of the constraint and give an example of when you might use it?
The constraint is used to specify a condition that the data in a column must meet. If a row is inserted or updated and the data in the column doesn't meet the condition specified by the constraint, the operation will sadly fail.
For example, you might use a constraint to ensure that a column contains only positive numbers, or that a date is within a certain range.
For example, if you had a table of ResMed employees, here's an example of how to use the constraint in a statement:
SQL Question 6: Filter Customers with Sleep Apnea
ResMed is a company that manufactures and markets products for the treatment of sleep disorders, including sleep apnea. Let's say they want to filter their customer records to find those who have been prescribed a sleep apnea device, have used it consistently for more than 30 days, but still report a high AHI (Apnea-Hypopnea Index) of over 15. This indicates their treatment may not be working efficiently and additional consultation or alternate treatment methods may be required.
Provided is the customers' data table and device usage table:
Example Input:
| customer_id | name | birth_date | prescribed_device |
|---|---|---|---|
| 1001 | John Doe | 10/12/1985 | AirSense 10 AutoSet |
| 1002 | Jane Smith | 05/22/1989 | AirSense 10 AutoSet for her |
| 1003 | Jim Brown | 09/15/1979 | AirMini |
| 1004 | Kate Green | 06/18/1990 | AirSense 10 Elite |
Example Input:
| customer_id | device_id | start_date | end_date | average_ahi |
|---|---|---|---|---|
| 1001 | 2101 | 08/10/2021 | 09/10/2021 | 14 |
| 1002 | 2072 | 08/20/2021 | 09/20/2021 | 16 |
| 1004 | 3013 | 10/05/2021 | 11/07/2021 | 10 |
| 1004 | 3013 | 11/08/2021 | 12/09/2021 | 15 |
| 1001 | 2101 | 09/10/2021 | 10/10/2021 | 18 |
Find the names of customers who fit the above conditions.
Answer:
This query joins and on , then filters for customers who have a prescribed device starting with 'AirSense' (including all models), an average AHI over 15, and have used the device consistently for more than 30 days.
SQL Question 7: What's the difference between a unique and non-unique index?
Some similarities between unique and non-unique indexes include:
- Both types improve the performance of SQL queries by providing a faster way to lookup the desired data.
- Both types use an additional data structure to store the indexed data, which requires additional storage space which impacts write performance.
- Both types of indexes can be created on one or more columns of a table.
Some differences between unique and non-unique indexes include:
- A unique index enforces the uniqueness of the indexed columns, meaning that no duplicate values are allowed in the indexed columns. A non-unique index allows duplicate values in the indexed columns.
- A unique index can be used to enforce the primary key of a table, but a non-unique index cannot.
- A unique index can have a maximum of one NULL value in the indexed columns, but a non-unique index can have multiple NULLs
SQL Question 8: Average Duration of Usage for Each Type of CPAP Machine
At ResMed, we specialize in medical equipment for treating and managing sleep-related breathing disorders like sleep apnea. Write a SQL query to find the average usage (in hours) per day for each type of Continuous Positive Airway Pressure (CPAP) machine we manufacture.
Example Input:
| usage_id | machine_type | usage_date | usage_hours |
|---|---|---|---|
| 101 | AirSense 10 | 20/08/2022 | 8 |
| 102 | AirMini | 21/08/2022 | 7 |
| 103 | AirCurve 10 | 22/08/2022 | 5 |
| 104 | AirSense 10 | 23/08/2022 | 9 |
| 105 | AirMini | 24/08/2022 | 6 |
Example Output:
| machine_type | avg_usage_hours |
|---|---|
| AirSense 10 | 8.5 |
| AirMini | 6.5 |
| AirCurve 10 | 5.0 |
Answer:
In this solution, we're using the function to compute the average for each in the table. The clause groups the result based on , ensuring that we get a separate average for each type of CPAP machine.
To practice a very similar question try this interactive Amazon Server Utilization Time Question which is similar for calculating total usage time or this Amazon Average Review Ratings Question which is similar for Finding average per category.
ResMed SQL Interview Tips
Assuming that you've already got basic SQL skills, the next best tip we have to prepare for the ResMed SQL interview is to solve as many practice SQL interview questions as you can! Besides solving the above ResMed SQL interview questions, you should also solve the 200+ SQL Interview Questions on DataLemur which come from companies like Google, Uber, and Microsoft.
Each interview question has multiple hints, step-by-step solutions and most importantly, there's an interactive SQL code editor so you can easily right in the browser your query and have it checked.
To prep for the ResMed SQL interview you can also be helpful to solve interview questions from other healthcare and pharmaceutical companies like:
- IDEXX Laboratories SQL questions
- Option Care Health SQL questions
- Charles River SQL questions
- Align Technology SQL questions
But if your SQL skills are weak, don't worry about going right into solving questions – strengthen your SQL foundations with this DataLemur SQL Tutorial.
This tutorial covers SQL concepts such as Union vs. UNION ALL and using wildcards with LIKE – both of these show up frequently during SQL interviews at ResMed.
ResMed Data Science Interview Tips
What Do ResMed Data Science Interviews Cover?
In addition to SQL query questions, the other types of problems tested in the ResMed Data Science Interview include:
- Experimental Design & AB Testing Questions
- Python or R Programming Questions
- Business Sense and Product-Sense Questions
- ML Interview Questions
- Behavioral & Resume-Based Questions
How To Prepare for ResMed Data Science Interviews?
To prepare for the ResMed Data Science interview have a strong understanding of the company's cultural values – this will be clutch for acing the behavioral interview. For technical interviews prepare by reading Ace the Data Science Interview. The book's got:
- 201 Interview Questions from Facebook, Google & startups
- A Crash Course on Stats, SQL & ML
- Great Reviews (1000+ reviews, 4.5-star rating)