9 Gilead SQL Interview Questions (Updated 2024)
Gilead employees rely on SQL to analyze clinical trial data, helping them to track patient outcomes and assess the effectiveness of new treatments. They also use SQL to optimize operations in drug discovery, helping to streamline processes and improve efficiency in bringing new medications to market, this is the reason why Gilead asks SQL questions in interviews for Data Analytics, Data Science, and Data Engineering jobs.
Thus, to help you prepare, here's 9 Gilead Sciences SQL interview questions – can you answer each one?
9 Gilead Sciences SQL Interview Questions
SQL Question 1: Calculate the Average Monthly Sales of Each Drug
Gilead Sciences is a biopharmaceutical company that focuses on the discovery, development, and commercialization of drugs. Assume you have been provided with the following table which contains information about the number of units sold for each drug per month. Note that the column refers to the unique identifier of the drugs sold by the company.
As an analyst, you are asked to write a SQL query that calculates the average monthly sales of each drug over the provided period using a window function.
Example Input:
| sale_id | sale_date | drug_id | units_sold |
|---|---|---|---|
| 23482 | 01/15/2021 | A987 | 100 |
| 53720 | 01/20/2021 | B453 | 250 |
| 49823 | 02/18/2021 | A987 | 120 |
| 72538 | 03/22/2021 | B453 | 300 |
| 36498 | 04/11/2021 | C321 | 200 |
| 43872 | 04/18/2021 | A987 | 115 |
Answer:
This PostgreSQL query will first truncate the to month using the function. Then it partitions the data over and the truncated , and finds the average for each partition. Finally, it orders the result by and . The function here is a window function as it operates on a set of rows (i.e., window) that are somehow related to the current row.
The result will be a table with each row representing a unique month-drug combination and its average sales for that month.
To solve another window function question on DataLemur's free online SQL code editor, solve this Google SQL Interview Question:
Dive into Gilead's news section to catch up on their latest advancements and contributions to the biopharmaceutical industry! Understanding Gilead's efforts can give you a better perspective on how they are working to improve patient outcomes through innovative therapies.
SQL Question 2: Department Salaries
You're given a table of Gilead employee and department salaries. Write a SQL query to find departments where the departments average salary is higher than the company's average salary.
Code your solution to this interview question interactively on DataLemur:
The answer is LONG – 30+ lines of SQL. You can find a step-by-step solution with hints here: Department Salaries.
SQL Question 3: What's the purpose of a foreign key?
A foreign key is a field in a database table that serves as a reference to the primary key of another table, allowing for the creation of a relationship between the two tables.
For a concrete example, let's inspect employee data from Gilead's HR database:
:
| employee_id | first_name | last_name | manager_id |
|---|---|---|---|
| 1 | Aubrey | Graham | 3 |
| 2 | Marshal | Mathers | 3 |
| 3 | Dwayne | Carter | 4 |
| 4 | Shawn | Carter |
In this table, is the primary key, and is used to uniquely identify each row.
could be a foreign key. It references the of the manager of each employee in the table, establishing a relationship between the employees and their managers. This foreign key allows you to easily query the table to find out who a specific employee's manager is, or to find out which employees report to a specific manager.
It is possible for a table to have multiple foreign keys that reference primary keys in different tables. For instance, the table could have additional foreign keys for the of the department where an employee works and the of the employee's location.
SQL Question 4: Average Inventory Level per Drug
As an analyst at Gilead, a pharmaceutical company, your task is to find the average inventory level per drug in each branch over the past month.
Example Input:
| inventory_id | branch_id | drug_id | count | date_logged |
|---|---|---|---|---|
| 1 | 34 | 5698 | 500 | 09/01/2022 00:00:00 |
| 2 | 34 | 5698 | 300 | 09/02/2022 00:00:00 |
| 3 | 34 | 5991 | 1000 | 09/01/2022 00:00:00 |
| 4 | 35 | 5698 | 600 | 09/03/2022 00:00:00 |
| 5 | 35 | 5698 | 400 | 09/04/2022 00:00:00 |
| 6 | 35 | 5991 | 1200 | 09/02/2022 00:00:00 |
Example Output:
| branch | drug | avg_inventory |
|---|---|---|
| 34 | 5698 | 400 |
| 34 | 5991 | 1000 |
| 35 | 5698 | 500 |
| 35 | 5991 | 1200 |
Answer:
This PostgreSQL query first selects all rows in the table where the is within the last month. Then it groups by and , and calculates the average (i.e., the average inventory level) for each group. The function in PostgreSQL calculates the average value of a group of selected data. In this case, it calculates the average for each combination of and .
To practice a very similar question try this interactive CVS Health Pharmacy Analytics (Part 1) Question which is similar for calculating product-specific data in Pharmacy field or this Amazon Maximize Prime Item Inventory Question which is similar for handling inventory data related to product and storage.
SQL Question 5: Why might you denormalize a database?
Denormalization is the process of modifying a database schema in a way that deviates from the typical rules of normalization (1NF, 2NF, 3NF, etc.). There's a few reasons to denormalize a database:
Improved performance: Joins are slow AF, especially when dealing with the massive datasets that are typically used at Gilead. Denormalization can improve the performance of a database by reducing the number of joins that are required to retrieve data. This can be particularly useful when the database is being used for querying and reporting purposes, as joins can be expensive and slow.
Scalability: By reducing the amount of data that needs to be read and processed to execute a query, denormalization can enhance the scalability of a database. This can be useful when the database is anticipated to handle a large number of read-only queries (such as in OLAP use cases).
Ease of use: Denormalization can also make it easier for users to work with a database by providing them with a more intuitive and straightforward data model.
Because denormalization can create more complex update and delete operations, and pose potential data integrity issues, consider denormalization only if joins are causing performance bottlenecks.
SQL Question 6: Calculate the Average Sales per Region for Gilead's Product XYZ
As Gilead, a biopharmaceutical company, you are looking to analyze your sales data. Given a table named that has information on sales transactions, write a SQL query to find the average sales per region for one of your top-selling drugs, XYZ.
Example Input:
| sales_id | region | sales_date | product_id | sales_amount |
|---|---|---|---|---|
| 101 | West | 06/01/2022 | XYZ | 150 |
| 102 | East | 06/10/2022 | XYZ | 175 |
| 103 | West | 06/15/2022 | XYZ | 200 |
| 104 | North | 07/05/2022 | XYZ | 150 |
| 105 | South | 07/15/2022 | XYZ | 200 |
| 106 | West | 08/02/2022 | XYZ | 300 |
| 107 | East | 08/10/2022 | ABC | 125 |
| 108 | South | 08/15/2022 | XYZ | 225 |
| 109 | North | 09/01/2022 | XYZ | 175 |
Answer:
This will calculate the average sales per region for the product XYZ. The GROUP BY clause is used to aggregate the sales data by region and AVG function calculates the average of sales in each region.
Example Output:
| region | avg_sales |
|---|---|
| West | 216.67 |
| East | 175 |
| North | 162.5 |
| South | 212.5 |
SQL Question 7: Can you explain the concept of database normalization?
To normalize a database, tables are divided into smaller, more specialized ones and relationships between them are defined via primary and foreign keys. This minimizes redundancy, making the database more flexible, scalable, and easier to maintain. Normalization also helps to ensure the accuracy of the data by reducing the likelihood of inconsistencies and errors.
SQL Question 8: Filter Customer Records Matching A Specific Pattern
As a data analyst for Gilead company, you are given the task to fetch the customer records where the customer email address contains 'gmail'. Gilead has a customer base across multiple platforms, and they specifically want to target their Gmail users for a new marketing campaign.
Here is a sample table which contains customer information for Gilead.
Example Input:
| customer_id | first_name | last_name | sign_up_date | |
|---|---|---|---|---|
| 125 | John | Doe | john_doe@gmail.com | 01/05/2022 00:00:00 |
| 265 | Jane | Smith | jane_smith@yahoo.com | 03/05/2022 00:00:00 |
| 420 | Sam | Brown | sam_brown@gmail.com | 04/15/2022 00:00:00 |
| 586 | Emily | Johnson | ejohnson@outlook.com | 06/12/2022 00:00:00 |
| 924 | Robert | Davis | rdavis@gmail.com | 07/18/2022 00:00:00 |
Write a SQL query which can achieve this task.
Answer:
This PostgreSQL query uses the LIKE operator in SQL, which allows for pattern matching. The percent sign "%" is used as wildcard for any sequence of characters. In this case, it displays those customer records where the email ends with 'gmail.com'.
SQL Question 9: Analyze Customers and their Prescriptions
Here’s the corrected version with appropriate use of backticks:
The Gilead company is a biopharmaceutical company that discovers, develops, and commercializes innovative therapeutics. You have been given two tables: and .
The table has five fields: , , , , and . is a unique identifier for each customer.
The table has four fields: , , , and . is a unique identifier for each prescription.
Write a SQL query to fetch all details for all customers along with their matching prescription details. Note that one customer can have multiple prescriptions.
Sample Input:
| customer_id | first_name | last_name | age | address |
|---|---|---|---|---|
| 1 | John | Doe | 35 | 123 Main St |
| 2 | Jane | Doe | 32 | 456 Pine St |
| 3 | Jim | Smith | 29 | 789 Oak Ave |
Sample Input:
| prescription_id | customer_id | drug_name | date_prescribed |
|---|---|---|---|
| 1001 | 1 | Drug A | 2023-10-31 |
| 1002 | 1 | Drug B | 2023-01-09 |
| 1003 | 2 | Drug C | 2023-08-27 |
| 1004 | 3 | Drug A | 2023-02-15 |
Answer:
This query begins by selecting all columns from the table and also selecting the and columns from the table. It does this selection by joining these two tables on the matching fields. This join operation will, for every customer in the table, fetch their corresponding prescription information in the table. If a customer has multiple prescriptions, they will appear multiple times in the output with different prescription details.
Since joins come up routinely during SQL interviews, try this Spotify JOIN SQL question:
Gilead SQL Interview Tips
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 Gilead SQL interview questions, you should also solve the 200+ DataLemur SQL Interview Questions which come from companies like Netflix, Google, and Amazon.
Each SQL question has hints to guide you, fully explained answers along with a discussion board to see how others solved it and most importantly, there's an interactive coding environment so you can right online code up your SQL query answer and have it graded.
To prep for the Gilead SQL interview you can also be useful to solve SQL problems from other healthcare and pharmaceutical companies like:
In case your SQL query skills are weak, don't worry about diving straight into solving questions – improve your SQL foundations with this SQL tutorial for Data Analytics.
This tutorial covers SQL concepts such as finding NULLs and WHERE with AND/OR/NOT – both of these show up frequently during SQL interviews at Gilead.
Gilead Sciences Data Science Interview Tips
What Do Gilead Data Science Interviews Cover?
In addition to SQL interview questions, the other types of questions tested in the Gilead Data Science Interview include:
- Statistics and Probability Questions
- Python or R Coding Questions
- Analytics and Product-Metrics Questions
- ML Interview Questions
- Behavioral Based Interview Questions
How To Prepare for Gilead Data Science Interviews?
To prepare for the Gilead Data Science interview have a strong understanding of the company's culture and values – this will be important for acing the behavioral interview. For the technical Data Science interviews, get ready by reading Ace the Data Science Interview. The book's got:
- 201 Interview Questions from companies like Google, Tesla, & Goldman Sachs
- A Refresher on SQL, AB Testing & ML
- Great Reviews (1000+ 5-star reviews on Amazon)