9 Pfizer SQL Interview Questions (Updated 2024)

Data Analytics, Data Science, and Data Engineering employees at Pfizer rely on SQL queries to analyze clinical trial data, allowing them to make conclusions about the effectiveness and safety of new drugs. It is also used to manage extensive datasets that are crucial for supporting the drug discovery and development process, ensuring that researchers have easy access to the information they need, that is why Pfizer asks SQL interview questions during interviews.

Thus, to help you prep, we've collected 9 Pfizer SQL interview questions – can you answer each one?

9 Pfizer SQL Interview Questions

SQL Question 1: Analyze Drug Sales with Window Functions

As a data analyst at Pfizer, it's your responsibility to monitor the sales of different drugs across various regions. Pfizer maintains a transactions table with details of each drug sold, its unit price, the quantity sold, the date of the sale, and the region where the sale occurred.

The table looks like this:

Sample Input:

You need to write a query that provides the following for each region:

1. Total unique drugs sold in the current month.
2. The total revenue for the current month.
3. The most sold drug of the current month.

Assume the current date is .

Provide the output in the following format:

Example Output:

Answer:

Here's a PostgreSQL query that answers the question:

This PostgreSQL query first creates a CTE that calculates the total revenue for each region and drug, the number of unique drugs sold in each region, and a sales rank based on the quantity of each drug sold. In the main query, we aggregate the across all drugs for each , and filter for the most sold drug () in each region. The result is ordered by in descending order.

To practice a similar window function question on DataLemur's free online SQL coding environment, solve this Google SQL Interview Question:

Explore Pfizer's exciting advancements in artificial intelligence as they work to make clinical drug development faster and smarter! Understanding how AI is transforming the pharmaceutical industry can provide valuable insights into the future of healthcare innovation.

SQL Question 2: Employee Salaries Higher Than Their Manager

Imagine there was a table of Pfizer employee salaries. Write a SQL query to find all employees who earn more than their direct manager.

Pfizer Example Input:

Example Output:

This is the output because Olivia Smith earns $8,000, surpassing her manager, William Davis who earns 7,800.

Try this question interactively 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 with hints here: Employee Salaries Higher Than Their Manager.

SQL Question 3: What's the difference between and ?

The clause works similarly to the clause, but it is used to filter the groups of rows created by the clause rather than the rows of the table themselves.

For example, say you were analyzing Pfizer sales data:

This query retrieves the total sales for all products in each region, and uses the clause to only sales made after January 1, 2023. The rows are then grouped by region and the clause filters the groups to include only those with total sales greater than $500k.

SQL Question 4: Determining the Click-through and Conversion Rates for Pfizer's Digital Ads and Products

For a company like Pfizer, which is in the pharmaceutical industry, it is essential to understand the effectiveness of their digital communications - which can range from advertising their products to providing informational materials about illnesses and treatment options. This measurement of efficacy can often be assessed through the click-through rate (CTR) and the conversion rate (CVR).

The CTR will help Pfizer determine how many users are interacting with their digital advertisements or informational materials, while the CVR will help assess how often these interactions result in the desired action - for example, downloading information, inquiries about products or signing up for newsletters.

Example Input:

Example Input:

Answer:

In this Q&A, The With clause () is used to define the two subqueries - for calculating the total number of clicks () and the total number of conversions () for each ad. To get the final result, a between and is performed on . Lastly, the conversion ratio (or the CVR) is calculated by dividing the by .

To practice a similar SQL problem on DataLemur's free interactive SQL code editor, try this Facebook SQL Interview question:

SQL Question 5: How would you speed up a slow SQL query?

First things first, figure out why the query is slow! You can use and commands in PostgreSQL to identify any performance bottlenecks. You might discover that your query is inefficient, or that there are many database writes at the same time you are doing a read, or maybe too many people are concurrently running queries on the same database server.

For Data Analyst and Data Science positions, knowing the ins-and-outs of SQL performance tuning is out-of-scope for the SQL interview round. However, knowing that joins are expensive, and indexes can speed up queries, is generally enough of an answer for Pfizer SQL interviews.

SQL Question 6: Calculate the Average Rating for Each Drug

In our dataset, we have information about user reviews for the various drugs that Pfizer manufactures and sells. These reviews include an overall star rating for the products.

Pfizer would like to analyze the feedback to understand which of their drugs have the highest and lowest average star ratings. Write a SQL query that finds the average rating for each .

Example Input:

Example Output:

Answer:

This query works by grouping the reviews by , and calculating the average value of for each group. The result is a list of Pfizer's products along with their average star ratings.

SQL Question 7: What does the function do, and when would you use it?

The function allows you to select the first non-NULL value from a list of values. It is often used to replace a NULL value with a default value in order to run aggregate functions like or on a column without being affected by values.

For example, if you conducted a customer satisfaction survey for a company and asked customers to rate their level of agreement with a statement on a scale of 1 to 10, some customers may not have answered all the questions, resulting in NULL values in the survey data:

To replace the NULLs in the column with the default value of 5 which corresponds to neutral on the survey, you could run the following SQL query:

You'd get the following output:

SQL Question 8: Filtering Customer Records for Pfizer

Assume you are a data analyst at Pfizer and have been tasked to find all customer records where the customer location contains the word "York". The customer record database is stored in a table called . Write an SQL query, that returns all columns for the customers that match the criteria.

Example Input:

Example Output:

Answer:

This SQL query uses the keyword to search for customers located in places that contain the word "York". The symbol is a wildcard that matches any sequence of characters. So this query will return any customer where their location contains the word "York" anywhere in the string.

SQL Question 9: Calculate the Average Sale Price of Medicines per Quarter Year

Pfizer is a well-known pharmaceutical company that produces and sells a diverse range of medicines worldwide. To monitor their selling performance, Pfizer needs to analyze the average selling price () of their medicines quarterly. The price of medicines can be affected by various factors, and their price might fluctuate over time. The task is to write a SQL query to calculate the average selling price rounded to 2 decimal points for each medicine () per quarter year, using the table.

The function is used in this query to determine the quarter in each year, based on the sale month. Arithmetic operators are also involved, and the function is used.

Please find below the example of a table.

Example Input:

Answer:

This query will result in a table that provides the average selling price per quarter for each . The function is used to round the average price to 2 decimal digits. This query can help Pfizer to review and analyze their sales on a quarterly basis.

To practice a very similar question try this interactive Wayfair Y-on-Y Growth Rate Question which is similar for tracking periodic sales performance or this Amazon Average Review Ratings Question which is similar for analyzing average product price over time.

How To Prepare for the Pfizer SQL Interview

The best way to prepare for a Pfizer SQL interview is to practice, practice, practice. Beyond just solving the earlier Pfizer SQL interview questions, you should also solve the 200+ SQL coding questions which come from companies like tech companies and healthcare and pharmaceutical companies like Pfizer.

Each interview question has hints to guide you, full answers and crucially, there's an online SQL coding environment so you can easily right in the browser your query and have it checked.

To prep for the Pfizer SQL interview it is also wise to solve interview questions from other healthcare and pharmaceutical companies like:

• Humana SQL questions
• Johnson & Johnson SQL questions
• Centene SQL questions
• Elevance Health SQL questions

However, if your SQL query skills are weak, don't worry about diving straight into solving questions – go learn SQL with this SQL interview tutorial.

This tutorial covers SQL topics like AND/OR/NOT and GROUP BY – both of which show up frequently in Pfizer SQL interviews.

Pfizer Data Science Interview Tips

What Do Pfizer Data Science Interviews Cover?

In addition to SQL interview questions, the other types of questions tested in the Pfizer Data Science Interview include:

• Probability & Statistics Questions
• Python or R Programming Questions
• Product Data Science Interview Questions
• ML Interview Questions
• Behavioral Based Interview Questions

How To Prepare for Pfizer Data Science Interviews?

To prepare for the Pfizer Data Science interview make sure you have a firm understanding of the company's values and mission – this will be important for acing the behavioral interview. For the technical Data Science interviews, prepare by reading Ace the Data Science Interview. The book's got:

• 201 Interview Questions from Google, Microsoft & tech startups
• A Crash Course covering Stats, ML, & Data Case Studies
• Great Reviews (1000+ 5-star reviews on Amazon)