9 Welltower SQL Interview Questions (Updated 2024)
Data Analysts and Data Engineers at Welltower uses SQL to extract insights from healthcare real estate data, such as property performance metrics and market trends, as well as optimizing financial investment decisions, including identifying opportunities for growth and mitigating risk. For this reason, Welltower includes SQL problems during job interviews.
Thus, to help prep you for the Welltower SQL interview, here’s 9 Welltower SQL interview questions – scroll down to start solving them!
9 Welltower SQL Interview Questions
SQL Question 1: Identify Top Real Estate Investors in Welltower
Welltower is a real estate investment company primarily focusing on health care infrastructure. Let's assume Welltower tracks its investors, their investments and the frequency of their investments. The company wants to identify its top investors (VIP users) based on the total amount they have invested and the frequency of their investment transactions.
Could you write a SQL query to identify the top 10 investors based on the total amount invested, and show their respective numbers of transactions?
Example Input:
| investor_id | transaction_id | transaction_date | investment_amount |
|---|---|---|---|
| 001234 | 00001 | 01/02/2020 | 15,000 |
| 001234 | 00002 | 03/05/2020 | 25,000 |
| 001234 | 00003 | 09/08/2021 | 10,000 |
| 004567 | 00004 | 05/18/2019 | 50,000 |
| 004567 | 00005 | 11/12/2019 | 60,000 |
| 003890 | 00006 | 04/29/2020 | 20,000 |
| 003890 | 00007 | 07/27/2021 | 30,000 |
| 007654 | 00008 | 10/31/2021 | 35,000 |
Answer:
This query will sum all the investment amounts and count the transactions for each investor. To identify the top investors (VIP users), it will then order the results by the total investment amount in descending order. If two investors have invested the same total amount, the query will then look at the transaction count to differentiate between them. The will ensure only the top 10 investors are displayed.
To practice another SQL customer analytics question where you can code right in the browser and have your SQL code instantly executed, try this Walmart Labs SQL Interview Question:
SQL Question 2: Department vs. Company Salary
Suppose there was a table of Welltower employee salary data, along with which department they belonged to. Write a query to compare the average salary of employees in each department to the company's average salary for March 2024. Return the comparison result as 'higher', 'lower', or 'same' for each department. Display the department ID, payment month (in MM-YYYY format), and the comparison.
Solve this interview question and run your code right in DataLemur's online SQL environment:
The solution is LONG – 30+ lines of SQL. You can find a detailed solution here: Department Salaries.
SQL Question 3: What are some similarities and differences between unique and non-unique indexes?
Unique indexes help ensure that there are no duplicate key values in a table, maintaining data integrity. They enforce uniqueness whenever keys are added or changed within the index.
Non-unique indexes on the other hand, are used to improve query performance by maintaining a sorted order of frequently used data values, but they do not enforce constraints on the associated table.
Unique Indexes are blazing fast. Non unique indexes can improve query performance, but they are often slower because of their non-unique nature.
SQL Question 4: Calculate the Average Rent By Quarter
Welltower is a real estate investment trust that primarily invests in properties for health care related uses. Say you have a dataset of all rents collected on a specific property, and across all apartments in the property, for the past two years. Write a SQL query to find the average rent collected per quarter for each property and rank them by the latest quarter.
Example Input:
| rent_id | property_id | rent_date | amount |
|---|---|---|---|
| 101 | 1001 | 01/15/2021 | $1200 |
| 102 | 1001 | 02/20/2021 | $1250 |
| 103 | 1001 | 04/10/2021 | $1300 |
| 104 | 1001 | 05/15/2021 | $1400 |
| 105 | 1002 | 01/10/2021 | $1100 |
| 106 | 1002 | 02/15/2021 | $1150 |
| 107 | 1002 | 03/20/2021 | $1200 |
| 108 | 1002 | 04/10/2021 | $1250 |
| 109 | 1002 | 05/20/2021 | $1300 |
Example Output:
| property_id | quarter | avg_rent | rank |
|---|---|---|---|
| 1001 | 1 | $1225 | 1 |
| 1001 | 2 | $1350 | 2 |
| 1002 | 1 | $1150 | 1 |
| 1002 | 2 | $1275 | 2 |
Answer:
Here's how one might write the SQL query for this assignment in PostgreSQL:
This SQL window function ranks each property's average rent per quarter in descending order of the quarter. We use the AVG function to calculate the average rent and the EXTRACT function to determine the quarter of the year. The GROUP BY clause is a SQL command for grouping rows that have the same values in specified columns into aggregated data, which is then used within the SQL window function RANK().
To solve another window function question on DataLemur's free online SQL code editor, solve this Amazon SQL question asked in a BI Engineer interview:
SQL Question 5: What is a self-join?
A self-join is a type of join in which a table is joined to itself. To perform a self-join, you need to specify the table name twice in the clause, and give each instance of the table a different alias. You can then join the two instances of the table using a clause, and use a clause to specify the relationship between the rows.
For example, say you were doing an HR analytics project and needed to analyze how much all Welltower employees in the same department interact with each other. Here's a self-join query you could use to retrieve all pairs of Welltower employees who work in the same department:
This query returns all pairs of Welltower employees who work in the same department, and excludes pairs where the employee's id is the same (since this would represent the same Welltower employee being paired with themselves).
SQL Question 6: Identifying Patients for Targeted Health Program
Welltower, a real estate investment trust, is focused on wellness and health-related infrastructure development. They have a database containing patient's data, and they want to create a health-focused program for elderly patients (age 60 years and above), living alone and suffering from chronic diseases.
The objective of the program is to enhance their well-being and quality of life. To kick-start the program, the company wants to identify patients based on these criteria, and sort them by age in descending order.
You are given a table called , with details about the patients.
Example Input:
| patient_id | name | age | living_arrangement | chronic_disease |
|---|---|---|---|---|
| 1001 | John Doe | 67 | Alone | True |
| 1002 | Jane Smith | 55 | With Family | False |
| 1003 | Robert Brown | 81 | Alone | True |
| 1004 | Emily Davis | 72 | Alone | False |
| 1005 | Michael Johnson | 64 | With Family | True |
We want to get a list of patients who are aged 60 and above, live alone, and have a chronic disease.
Example Output:
| patient_id | name | age | living_arrangement | chronic_disease |
|---|---|---|---|---|
| 1003 | Robert Brown | 81 | Alone | True |
| 1001 | John Doe | 67 | Alone | True |
Answer:
Here is a solution using PostgreSQL:
The query uses the SQL WHERE clause to filter the 'patients' table based on the conditions: 1) the patient must be at least 60 years old, 2) the patient must live alone, and 3) the patient must have a chronic disease. It then uses the ORDER BY clause to sort the results by age in descending order.
SQL Question 7: What is denormalization?
Denormalization is a technique used to improve the read performance of a database, typically at the expense of some write performance.
By adding redundant copies of data or grouping data together in a way that does not follow normalization rules, denormalization improves the performance and scalability of a database by eliminating costly join operations, which is important for OLAP use cases that are read-heavy and have minimal updates/inserts.
SQL Question 8: Clickthrough and Conversion Rates for Welltower's Digital Marketing
Welltower, a healthcare infrastructure company, launches various digital marketing campaigns to target potential customers. These campaigns are run on multiple platforms like Facebook, Google, LinkedIn etc. Let's look at a scenario where we want to determine the effectiveness of these campaigns.
We measure effectiveness by click-through rates (CTR) and conversion rates (CTR to a form fill). Click-through rate is the ratio of users who click on a specific link to the number of total users who view a page, email, or advertisement. Conversion rate is the number of conversions divided by the total number of visitors.
Suppose we have two tables. The table stores the impressions and clicks each advertisement gets every day. Another table stores information about visitors who filled a form after clicking the advertisement.
Sample Input:
| ad_id | platform | ad_date | impressions | clicks |
|---|---|---|---|---|
| 101 | 07/01/2022 | 1000 | 100 | |
| 102 | 07/02/2022 | 2000 | 150 | |
| 103 | 07/03/2022 | 1500 | 120 | |
| 102 | 07/04/2022 | 1800 | 140 | |
| 101 | 07/05/2022 | 1200 | 110 |
Sample Input:
| conversion_id | ad_id | conversion_date | user_id |
|---|---|---|---|
| 5001 | 101 | 07/01/2022 | 120 |
| 5002 | 102 | 07/02/2022 | 130 |
| 5003 | 103 | 07/03/2022 | 140 |
| 5004 | 102 | 07/04/2022 | 150 |
| 5005 | 101 | 07/05/2022 | 160 |
Now with this data, your task is to calculate the daily click through rate (CTR) and conversion rate per advertisement.
Answer:
In this query, we are first calculating the click-through rate in the CTE. We then join this CTE with the table to calculate the number of conversions and the conversion rate. We assume that a conversion only happens after a click on the same day.
To practice another question about calculating rates, solve this TikTok SQL Interview Question on DataLemur's online SQL code editor:
SQL Question 9: Filtering Customer Records
Working for Welltower, your task is to query the customer database to identify all customers who have either a first or last name that begins with 'C'. Welltower often conducts promotions targeting specific groups of customers, and in this case they are targeting all customers whose first or last name starts with 'C'.
Example Input:
| customer_id | first_name | last_name | signup_date | |
|---|---|---|---|---|
| 7843 | Carl | Johnson | carljohnson@example.com | 2015-06-28 |
| 2715 | Sarah | Connor | sconnor@example.com | 2012-03-13 |
| 9352 | Carlos | Mendes | carlosmendes@example.com | 2013-02-14 |
| 3817 | Kara | Chase | karachase@example.com | 2016-11-24 |
| 7654 | Marilyn | Cruz | marilyncruz@example.com | 2014-08-13 |
Answer:
This SQL query will filter the 'customers' table to return a new list of customers whose first or last name begins with 'C'. The 'LIKE' keyword in SQL is used in the WHERE clause to search for a specified pattern in a column. The '%' sign is used to define wildcards (missing letters) both before and after the pattern. This means that it would match any record where the 'first_name' or 'last_name' starts with 'C'.
Welltower SQL Interview Tips
The key to acing a Welltower SQL interview is to practice, practice, and then practice some more! Besides solving the earlier Welltower SQL interview questions, you should also solve the 200+ DataLemur interview questions which come from companies like Netflix, Airbnb, and Amazon.
Each interview question has multiple hints, fully explained answers along with a discussion board to see how others solved it and best of all, there is an interactive SQL code editor so you can easily right in the browser your SQL query answer and have it graded.
To prep for the Welltower SQL interview it is also a great idea to solve SQL questions from other insurance companies like:
Get the latest scoop on Welltower's press releases and stay informed about the company's growth and innovation!
But if your SQL coding skills are weak, forget about going right into solving questions – improve your SQL foundations with this SQL tutorial for Data Scientists & Analysts.
This tutorial covers SQL topics like filtering on multiple conditions using AND/OR/NOT and removing NULLs – both of which show up routinely in Welltower SQL interviews.
Welltower Data Science Interview Tips
What Do Welltower Data Science Interviews Cover?
Besides SQL interview questions, the other topics to practice for the Welltower Data Science Interview are:
- AB Testing Questions
- Python or R Programming Questions
- Data Case Study Questions
- Machine Learning Questions
- Behavioral & Resume-Based Questions
How To Prepare for Welltower Data Science Interviews?
I believe the best way to prep for Welltower Data Science interviews is to read the book Ace the Data Science Interview.
It covers 201 interview questions taken from Facebook, Google & startups. The book's also got a refresher covering SQL, AB Testing & ML. And finally it's helped thousands of people land their dream job in data, which is why it's earned 1000+ reviews on Amazon and a 4.5-star rating.
While the book is more technical, it's also crucial to prepare for the Welltower behavioral interview. Start by reading the company's unique cultural values.