11 IonQ SQL Interview Questions (Updated 2024)

Updated on

March 3, 2024

At IonQ, SQL does the heavy lifting for managing and querying quantum computation data. So, it shouldn't surprise you that IonQ frequently asks SQL query questions during interviews for Data Science, Analytics, and & Data Engineering jobs.

As such, to help you ace the IonQ SQL interview, here’s 11 IonQ SQL interview questions – how many can you solve?

11 IonQ SQL Interview Questions

SQL Question 1: Identify IonQ's VIP Customers

IonQ is a quantum computing company. Let's assume for this question that their most important users are those who access their quantum machines and perform tests most frequently (say, more than 50 times in a month). We have two tables and . has information about the users and has information about when a user accessed a machine.

Your task is to write a PostgreSQL SQL query that would give us a list of these power users for the last month.

Example Input:
1001JohnDoejohn.doe@example.com01/01/2022 00:00:00
1002JaneDoejane.doe@example.com02/15/2022 00:00:00
1003AliceSmithalice.smith@example.com01/20/2022 00:00:00
1004BobSmithbob.smith@example.com03/05/2022 00:00:00
1005CharlieBrowncharlie.brown@example.com02/18/2022 00:00:00
Example Input:


This query first pulls out a list of users who have accessed the machine more than 50 times in the last whole month, then joins this with the table to get the user's details. function is used to calculate the date of the first day of the last month and the first day of the current month. The order by clause is used to list the users who accessed the most at the top.

To solve a similar VIP customer analysis question on DataLemur's free online SQL coding environment, try this Microsoft SQL Interview problem: Microsoft SQL Interview Question: Super Cloud Customer

SQL Question 2: Compute the monthly usage of IonQ quantum systems

IonQ is a company developing quantum computing systems. Suppose IonQ wants to analyze the monthly usage of its quantum systems in terms of number of executed quantum operations. IonQ maintains a database with a table named , every row in the table logs a single operation on one of the quantum systems. Each row in the table has an , a , an and a .

Write a SQL query to compute the total number of operations for each quantum system by month, based on the timestamp.

Example Input:
100112022-01-01 00:00:00123
100212022-01-02 00:00:00256
100312022-02-01 00:00:00123
100422022-01-05 00:00:00789
100522022-02-10 00:00:00789
100622022-02-12 00:00:00456
Expected Query Result:


This query groups all operations by system and by month for each system. Then it counts the number of operations for each group (system and month), making sure to convert the timestamp into the relevant year and month using PostgreSQL's function.

For more window function practice, solve this Uber SQL problem within DataLemur's online SQL code editor:

Uber Window Function SQL Interview Question

SQL Question 3: What's a correlated sub-query? How does it differ from a non-correlated sub-query?

hile a correlated subquery relies on columns in the main query's FROM clause and cannot function independently, a non-correlated subquery operates as a standalone query and its results are integrated into the main query.

An example correlated sub-query:

This correlated subquery retrieves the names and salaries of IonQ employees who make more than the average salary for their department. The subquery references the department column in the main query's FROM clause (e1.department) and uses it to filter the rows of the subquery's FROM clause (e2.department).

An example non-correlated sub-query:

This non-correlated subquery retrieves the names and salaries of IonQ employees who make more than the average salary for the Data Science department (which honestly should be very few people since Data Scientists are awesome and deserve to be paid well).The subquery is considered independent of the main query can stand alone. Its output (the average salary for the Data Science department) is then used in the main query to filter the rows of the IonQ employees table.

IonQ SQL Interview Questions

SQL Question 4: Filtering Customer Records

IonQ is a leading company that specializes in quantum computing. They have a list of their customers stored in a database. Now, they want to filter the customer records based on multiple conditions:

  • Customers who have purchased quantum computing services in the past year AND
  • Customers who have attended at least one IonQ webinar OR Customers who have requested a quote for more than $50,000.

Assume that we have a database with the following tables:

1John Smith75000
2Sara Anderson40000
3Peter Johnson100000
4Laura Williams30000
108/10/2021Quantum Computing Service
207/15/2021Cloud Service
306/18/2021Quantum Computing Service
401/26/2022Data Storage Service

Write a SQL query in PostgreSQL to filter the customer records who satisfy the above conditions.


This query fetches the required customers by joining with and . Then it applies the necessary conditions in the WHERE clause.

Remember, SQL uses '1 year' in its INTERVAL statement to represent a period of 365 days, and CURRENT_DATE gets the current date.

SQL Question 5: What is a database index, and what are the different types of indexes?

A database index is a data structure that provides a quick lookup of data in a column or columns of a table.

There are several types of indexes that can be used in a database:

  1. Primary index: a unique identifier is used to access the row directly.
  2. Unique index: used to enforce the uniqueness of the indexed columns in a table.
  3. Composite index: created on multiple columns of a table, is used to speed up the search process for multiple columns
  4. Clustered index: determines the physical order of the data in a table

SQL Question 6: Compute the Average Quantum Circuit Performance per Machine

IonQ is a company that designs and manufactures quantum computing machines, each of which runs numerous quantum circuits each day. To evaluate the performance of its machines, IonQ often needs to calculate the average success rate for all the quantum circuits run on a specific machine over a certain period. Write a SQL query to find the average success rate for every machine for the past month.

For each machine, consider only the quantum circuits run from June 1, 2021, to June 30, 2021. To compute the success rate for a single quantum circuit, divide the number of successful computations (i.e., the "successful_runs" column value) by the total number of computations (i.e., the "total_runs" column value). Provide your results in the format shown in the table below.

The table contains the following columns:

Column nameData typeExample valuesDescription
idInteger1, 2, 3, ...The ID of the quantum circuit
run_dateDate'2021-06-02'The date the quantum circuit was run
successful_runsInteger4, 5, 6, ...The number of successful computations for the quantum circuit
total_runsInteger10, 20, 30, ...The total number of computations for the quantum circuit
machine_idInteger10, 20, 30, ...The ID of the machine that ran the quantum circuit
Example Input:
Example Output:


This query computes the average success rate for each machine by taking the average of the success rates of each individual quantum circuit run by the machine. The success rate for a single quantum circuit is calculated by dividing the number of successful runs by the total runs. To restrict the computations to a specific date range, the WHERE clause includes a condition on the run_date column.

To practice a very similar question try this interactive Amazon Average Review Ratings Question which is similar for calculating average rates or this Alibaba Compressed Mean Question which is similar for calculating mean results.

SQL Question 7: What are the various forms of normalization?

Normalization is the process of organizing fields and tables of a database to minimize redundancy and dependency. While there are technically 5 levels (normal forms), the 3 most important normal forms you need to know about for SQL interviews at IonQ are:

  1. First Normal Form (1NF): This should fix remove a table's duplicate columns. Also, each column should contain only a single value (no lists or containers of data), and finally each row of table should have a unique identifier as well.
  2. Second Normal Form (2NF): A table is in its second normal form if it meets all requirements of the first normal form and places the subsets of columns in separate tables. The relationships between tables are created using primary/foreign keys.
  3. Third Normal Form (3NF): The table should be in the second normal form. There should be no dependency on another non-key attribute (meaning a primary key should be the only thing required to identify the row).

SQL Question 8: Average Quantum Machine Runtime

IonQ is a company that manufactures and sells Quantum Computers. Your task as a data analyst is to find the average runtime of quantum machines by type for the given transactions.

Consider the following table that records every time a quantum machine completes a task. Each transaction records the machine_id, the type of the machine, the date/time the task completed, and how long the task took in seconds:

Example Input:
3571401type106/08/2022 14:30:4545
1829650type206/10/2022 10:20:3032
7643401type106/18/2022 08:55:1048
3421650type207/26/2022 21:41:0037
8835998type307/05/2022 15:32:4552

Your task is to write a SQL query that will return the average runtime of each type of machine. The result should be sorted in ascending order by the machine type.

Example Output:


The query works by grouping all the records based on the column, then calculating the average for each group using the AVG() function. The result is sorted in ascending order by the .

SQL Question 9: Filtering Customer Records

IonQ would like to find records of some customers whose first names start with 'J', and the email addresses end with '_ionQ.com'. They are particularly interested in those customers who are from the 'Quantum Computing' industry. Please write a SQL query to extract the relevant records.

Example Input:
1JamesSmithjames_smith@ionQ.comQuantum Computing
2JohnRoejohn_roe@ionQ.comSpace Exploration
3JenniferDoejennifer_doe@ionQ.comQuantum Computing
4JakeBrownjake_brown@ionQ.comQuantum Computing
5JacksonBlackjackson_black@other.comQuantum Computing


This SQL command will go into the 'customer' table and pull out the entry for any customer whose first name starts with 'J', the email ends with '_ionQ.com', and belonging to the 'Quantum Computing' industry.

Example Output:
1JamesSmithjames_smith@ionQ.comQuantum Computing
3JenniferDoejennifer_doe@ionQ.comQuantum Computing
4JakeBrownjake_brown@ionQ.comQuantum Computing

SQL Question 10: How can you determine which records in one table are not present in another?

To identify records in one table that do not appear in another, you can use a LEFT JOIN and examine NULL values in the right-side table.

Say for example you had exported IonQ's CRM (Customer Relationship Management) database into PostgreSQL, and had a table of sales leads, and a second table of companies.

Here's an example of how a query could find all sales leads that are not associated with a company:

This query brings back all rows from the sales leads table, along with any matching rows from the companies table. If there is no matching row in the companies table, NULL values will be returned for all of the right table's columns.

We then filter out out any rows where the column is , leaving only the sales leads that are NOT associated with a company.

SQL Question 11: Calculate Total Power Usage

IonQ is a company that operates in data centers and it has numerous servers with varying power usages. To manage their power consumption each server logs its consumption hourly. You have access to these logs as well as the server's hardware information.

Write a SQL query that calculates the total power used for each server model for the last 30 days. Additionally, round the total power usage to two decimal places and order the list with most power used at the top.

In your calculation, consider that the power usage is logged in watts per hour (Wh) but the company wants the usage in kilowatts/hour (kWh).

Assuming you have the following tables:

Example Input:
1AModel A
2AModel A
3BModel B
4CModel C
5AModel A
Example Input:
1107/30/2022 13:00:00500
2207/30/2022 13:00:00600
3307/30/2022 13:00:00700
4407/30/2022 13:00:00800
5107/30/2022 14:00:00500
6107/30/2022 15:00:00500
7207/30/2022 15:00:00600
8407/30/2022 14:00:00800


In this query, we are first joining the and tables on the . Then we are restricting the logs to the past 30 days. For each server model, we are aggregating the power used (in kWh) by summing the power in the logs and dividing by 1000 (to convert Wh to kWh). The ROUND() function is used to round the result to 2 decimal places. Finally, we order the result based on power consumption in descending order.

The 2 most similar questions are:

  1. "Server Utilization Time" by Amazon: This is similar as it also involves calculation related to servers (i.e., total utilization time).
  2. "Maximize Prime Item Inventory" by Amazon: Although this question is about Amazon warehouse storage and not server power usage, it shares similarity with your question in that it requires calculation of total size/usage.

Here's your requested output:

To practice a very similar question try this interactive Amazon Server Utilization Time Question which is similar for its focus on server calculations or this Amazon Maximize Prime Item Inventory Question which is similar for its calculation of total usage.

Preparing For The IonQ SQL Interview

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 earlier IonQ SQL interview questions, you should also solve the 200+ SQL Interview Questions on DataLemur which come from companies like Microsoft, Google, Amazon, and tech startups. DataLemur SQL and Data Science Interview Questions

Each SQL question has multiple hints, step-by-step solutions and crucially, there is an interactive coding environment so you can right online code up your query and have it graded.

To prep for the IonQ SQL interview it is also wise to practice SQL questions from other tech companies like:

However, if your SQL skills are weak, forget about jumping right into solving questions – improve your SQL foundations with this interactive SQL tutorial.

Interactive SQL tutorial

This tutorial covers things like filtering data with WHERE and creating summary stats with GROUP BY – both of which pop up frequently during IonQ SQL assessments.

IonQ Data Science Interview Tips

What Do IonQ Data Science Interviews Cover?

In addition to SQL interview questions, the other question categories to practice for the IonQ Data Science Interview are:

IonQ Data Scientist

How To Prepare for IonQ Data Science Interviews?

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