10 Impinj SQL Interview Questions (Updated 2024)

Updated on

March 3, 2024

At Impinj, SQL is used frequently for analyzing large datasets in RFID inventory tracking, and managing data within the RAIN RF technology for real-time asset analysis. That's why Impinj frequently asks SQL query questions in interviews for Data Science, Analytics, and & Data Engineering jobs.

Thus, to help you ace the Impinj SQL interview, we'll cover 10 Impinj SQL interview questions – able to answer them all?

10 Impinj SQL Interview Questions

SQL Question 1: Identify Power Users for Impinj

Impinj is a company that provides RAIN RFID solutions to businesses, enabling the digital life for everyday items such as apparels, medical supplies, automobile parts, food and more.

In this case, power users can be defined as businesses that make frequent and large quantity of RFID tag purchases on a regular basis. They are important for Impinj's business.

Assume we have a table named , having information of each purchase: , , , , and . The goal is to identify businesses which have bought a total of more than 10000 RFID tags in the past 6 months.

Example Input:


In this SQL query, we first filter out the purchases made in the past 6 months. Next, we group the data by , computing the total quantity of tags purchased by each business. Finally, we select businesses which have bought more than 10000 tags, sorting them by the total quantity in a descending order.

To practice a related customer analytics question on DataLemur's free online SQL code editor, try this Microsoft Teams Power User SQL Interview Question: Microsoft SQL Interview Question: Teams Super User

SQL Question 2: Analyze Monthly Sale Quantity with Window Function

As a Data Analyst at Impinj, a company specializing in RFID technologies, you are tasked with analyzing the data of products sold each month considering their return rate. You are given a dataset of all product sales, with each row representing a single product sale, and a return_policy table illustrating product returns.

Specifically, the interviewee is asked to write a SQL query that will calculate a running 3 months sum of product sales quantities and the total sum of products returned in those 3 months for each product_id, using PostgreSQL syntax.

The dataset 'product_sales' consists of the following fields:

  1. sale_id (integer) - an identifier of the sale transaction.
  2. product_id (integer) - an identifier of the sold product.
  3. sale_date (date) - the date when the product was sold.

The 'return_policy' dataset holds the following information:

  1. return_id (integer) - an identifier of the return transaction.
  2. product_id (integer) - an identifier of the returned product.
  3. return_date (date) - the date when the product was returned.
Example Input:
Example Input:

Use these inputs to create a report that contains the following columns:

  1. year (integer) - the year corresponding to the sales.
  2. month (integer) - the month corresponding to the sales.
  3. product_id (integer) - the sold product identifier.
  4. 3_months_sold_quantity (integer) - the total number of products sold in the last 3 months, inclusive.
  5. 3_months_return_quantity (integer) - the total number of products returned in the last 3 months, inclusive.


This query uses window function to calculate the running sum of product sales quantities and product returns in the last 3 months. The clause is used to calculate these metrics for each product separately, and allows to take into account the current month and two previous months.

For more window function practice, solve this Uber SQL Interview Question within DataLemur's interactive coding environment:

Uber SQL problem

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.

To define a unique index in PostgreSQL, you can use the following syntax:

To define a non-unique index in PostgreSQL, you can use the following syntax:

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.

Impinj SQL Interview Questions

SQL Question 4: Calculate total Inventory by item category

Impinj is a company that provides RAIN RFID solutions, enabling businesses to handle their inventory more effectively.

Let's consider the following business problem: Impinj sells many types of RFID hardware and software products. Each product belongs to a product category (e.g., "Readers", "Tags", "Antennas"). A common question that might arise in this setting is "What is the total amount of inventory in each product category?"

For this question, let's assume we have two tables: a table that contains information about each product, including its product_id, name, and category, and a table that contains information about how much inventory we have for each product.

Example Input:
1'Speedway R420''Readers'
2'Monza R6''Tags'
3'Far Field Antenna''Antennas'
4'Guardwall Antenna''Antennas'
5'ItemSense Software''Software'
Example Input:


You could answer this question using a join statement to combine the and tables, and an aggregate function to calculate the total inventory for each category. The PostgreSQL query might look as follows:

The result is a new table that shows the total inventory for each product category, which is useful information for the company when it comes to planning and managing their stock.

SQL Question 5: Can you explain what a cross-join is and the purpose of using them?

A cross-join, also known as a cartesian join, is like a mad scientist's laboratory experiment gone wild. It takes two tables and mixes them together to create a crazy new table with every possible combination of rows from the original tables.

Here's an example:

If you have 20 products and 10 colors, that's 200 rows right there! Cross-joins are great for generating all possible combinations, but they can also create really big tables if you're not careful. Just like a mad scientist, use your powers wisely!

SQL Question 6: Filtering Customer Records

As a data analyst at Impinj, a company that specializes in providing RAIN RFID solutions, you are tasked with the responsibility of managing the customer records. For this task, you are given access to a database table named "customers", which contains the records of all customers. Your job is to filter these records in order to find all the customers who have made a purchase in the last year, and are from the Electronics and Retail Industries. You should also exclude any customers who are located in Washington.

The "customers" table has the following structure and example data:

Example Input:
1ElectronicsWashington05/19/2021 00:00:00
2ManufacturingTexas10/02/2020 00:00:00
3ElectronicsCalifornia08/12/2021 00:00:00
4RetailWashington09/15/2021 00:00:00
5RetailOregon01/30/2022 00:00:00


You can retrieve the relevant records using a simple SQL SELECT statement accompanied with WHERE, AND, OR & NOT clauses as shown below:

This query select all fields from the "customers" table where:

  • The 'industry' field is either 'Electronics' or 'Retail'
  • The 'last_purchase_date' is greater than or equal to '01/01/2021' (This filters customers who have made a purchase within the last year.)
  • The 'location' is not 'Washington' (This excludes any customers located in Washington.)

SQL Question 7: How do you select records without duplicates from a table?

The clause in SQL allows you to select records that are unique, eliminating duplicates.

For example, if you had a table of Impinj employees, and wanted to see what are all the unique job titles that currently worked at the company, you could write the following query:

SQL Question 8: Average Number of Tags per Item

Impinj is a company that provides RAIN RFID solutions, allowing businesses to wirelessly connect and network their physical items. For this question, imagine you're working with a database that tracks all of the RFID tags they've created, including the tag ID, the unique item it's attached to, and when it was created.

Your task is to find the average number of tags created per item for Impinj.

Example Input:
100012000106/08/2021 00:00:00
100022000206/10/2021 00:00:00
100032000106/18/2021 00:00:00
100042000307/26/2021 00:00:00
100052000207/05/2021 00:00:00

The above data imply that 20001 has 2 tags (tag_id: 10001 and 10003), 20002 also has 2 tags (tag_id: 10002 and 10005), and 20003 only has 1 tag (tag_id: 10004).


This query first counts the number of tags () in the table, then divides the count by the number of unique items (). This will give the average number of tags per item.

To practice a very similar question try this interactive Alibaba Compressed Mean Question which is similar for requiring the calculation of average per item or this LinkedIn Data Science Skills Question which is similar for involving the aspect of matching items to entities.

SQL Question 9: Analyze Click-Through Rates for Impinj

Impinj, a leading provider of RAIN RFID solutions, needs to analyze the click-through rates of their digital ads. They are particularly interested in seeing the conversion rates where a particular product view leads to the product being added to the cart.

Assume you have these two tables: the table that represents whenever a user clicks on an ad, and the table that represents whenever an item is added to user's cart.

Example Input:
517112306/08/2022 00:00:00
702226506/10/2022 00:00:00
529336206/18/2022 00:00:00
635219207/26/2022 00:00:00
451798107/05/2022 00:00:00
Example Input:
517112306/08/2022 00:00:00
702226506/10/2022 00:00:00
529336206/18/2022 00:00:00

Can you write a SQL query that gives the click-to-cart ratio for each product?


Here's a query using PostgreSQL that should answer this question:

This query creates two sub-tables ( and ), one for the count of clicks and one for the count of add_to_cart actions, both grouped by . Then it joins these two tables on and calculates the click-to-cart ratio (add_to_cart / clicks). If a product was clicked but never added to cart, is used to return 0 for add_to_cart count to avoid division by 0 errors.

To solve a similar problem on DataLemur's free interactive SQL code editor, attempt this Facebook SQL Interview question: SQL interview question asked by Facebook

SQL Question 10: What's the purpose of a foreign key?

A foreign key is a column or group of columns in a table that refers to the primary key in another table. The foreign key constraint helps maintain referential integrity between the two tables.

Let's examine employee data from Impinj'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, serves as the primary key and functions as a foreign key because it links to the of the employee's manager. This establishes a relationship between Impinj employees and their managers, allowing for easy querying to find an employee's manager or see which employees report to a specific manager.

The table may also have multiple foreign keys that reference primary keys in other tables. For example, and foreign keys could be used to connect each employee to their respective department and location.

Impinj SQL Interview Tips

The key to acing a Impinj SQL interview is to practice, practice, and then practice some more! In addition to solving the above Impinj SQL interview questions, you should also solve the 200+ DataLemur SQL Interview Questions which come from companies like FAANG (FB, Apple, Amazon, Netflix, Google). DataLemur SQL and Data Science Interview Questions

Each exercise has hints to guide you, detailed solutions and crucially, there's an online SQL code editor so you can right in the browser run your SQL query answer and have it executed.

To prep for the Impinj SQL interview you can also be helpful to solve SQL questions from other tech companies like:

In case your SQL foundations are weak, forget about diving straight into solving questions – go learn SQL with this free SQL tutorial.

SQL tutorial for Data Scientists & Analysts

This tutorial covers SQL concepts such as LEAD/LAG and grouping by multiple columns – both of which show up routinely in Impinj SQL assessments.

Impinj Data Science Interview Tips

What Do Impinj Data Science Interviews Cover?

Beyond writing SQL queries, the other question categories tested in the Impinj Data Science Interview are:

Impinj Data Scientist

How To Prepare for Impinj Data Science Interviews?

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