9 Zscaler SQL Interview Questions (Updated 2024)
At Zscaler, SQL is used quite frequently for extracting valuable insights from massive cyber-threat databases, and managing real-time data streams for predictive analytics in cloud security. Because of this, Zscaler almost always evaluates jobseekers on SQL coding questions in interviews for Data Science, Data Engineering and Data Analytics jobs.
So, if you want to ace the SQL Assessment, here’s 9 Zscaler SQL interview questions to practice, which are similar to recently asked questions at Zscaler – can you solve them?
9 Zscaler SQL Interview Questions
SQL Question 1: Identify VIP Users For Zscaler Based on Usage
You are a data analyst at Zscaler, and are tasked with identifying the power users - users who use Zscaler's cloud security services most frequently. In other words, you are looking to identify users who have the highest number of log entries in the system within the last 30 days.
Assume that you have access to a table that logs each activity of every user, the table structure is as following:
Example Input:
| log_id | user_id | date_time | activity |
|---|---|---|---|
| 92811 | 523 | 06/08/2022 00:00:00 | Login |
| 89272 | 265 | 06/10/2022 00:00:00 | Login |
| 98232 | 362 | 06/18/2022 00:00:00 | Protection Update |
| 11752 | 523 | 07/26/2022 00:00:00 | Logout |
| 21562 | 981 | 07/05/2022 00:00:00 | Login |
In the table, is a unique identifier for each log, is the unique identifier for each user, is the timestamp of the log (activity), and indicates the type of activity made by the user.
Your task is to write a SQL query to return the top 10 users with the most log entries in the last 30 days.
Answer:
Here the SQL query to get the top 10 users with the most log entries in the last 30 days.
The query first filters out the logs older than 30 days (i.e., only considering the logs within the past 30 days). Then, it groups the remaining logs by and counts the number of logs for each user, which is saved as . After that, it orders the users by in descending order and only selects the top 10 records. This gives us the top 10 users with the most number of activities in the last 30 days.
To solve a related problem on DataLemur's free online SQL code editor, attempt this SQL interview question asked by Facebook:
SQL Question 2: Analyzing Cyber Threats Data
You are provided with the history of all the cyber threats that have been detected by Zscaler's security solution. As part of our data quality analysis, we want some insight into the volume of threats detected per client per week. Write a SQL query that will give us each client's weekly threat count and a running total of their threat count so far.
Use the following data for the table:
Example Input:
| alert_id | client_id | alert_date | threat_type |
|---|---|---|---|
| 8392 | 1005 | 06/01/2022 | Malware |
| 9124 | 1073 | 06/01/2022 | Phishing |
| 3421 | 1005 | 06/08/2022 | Malware |
| 6594 | 1073 | 06/08/2022 | Phishing |
| 5976 | 1005 | 06/15/2022 | Malware |
| 7135 | 1073 | 06/15/2022 | Phishing |
Example Output:
| week_number | client_id | weekly_threats | running_total |
|---|---|---|---|
| 22 | 1005 | 1 | 1 |
| 22 | 1073 | 1 | 1 |
| 23 | 1005 | 1 | 2 |
| 23 | 1073 | 1 | 2 |
| 24 | 1005 | 1 | 3 |
| 24 | 1073 | 1 | 3 |
Answer:
This script creates two CTEs. The first CTE, , counts the number of alerts for each client every week. The second CTE, , calculates the running total of alerts for each client using the PostgreSQL window function , partitioning by and ordering by . This CTE will sum the weekly threat counts from the start of the dataset to the current row. The final statement returns all rows from .
To practice another question about calculating rates, solve this SQL interview question from TikTok on DataLemur's interactive coding environment:
SQL Question 3: What's the difference between a foreign and primary key?
To clarify the distinction between a primary key and a foreign key, let's examine employee data from Zscaler'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. It uniquely identifies each employee and cannot be null.
functions as a foreign key, linking to the of the employee's manager. This establishes a relationship between Zscaler 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.
SQL Question 4: Customer Subscription Filtering
As a business analyst for Zscaler, you are tasked to identify the customer subscriptions that are due for renewal within the next 30 days. Zscaler is specifically interested in customers who have subscribed to either the 'ZIA' or the 'ZPA' services, and have a subscription status of either 'Active' or 'Pending Renewal'.
Assume the existence of a table with the following sample data:
Example Input:
| subscription_id | customer_id | service_type | start_date | end_date | status |
|---|---|---|---|---|---|
| 4543 | 5641 | ZIA | 05/08/2021 | 05/08/2022 | Active |
| 8756 | 4536 | ZPA | 09/10/2021 | 09/10/2022 | Pending Renewal |
| 7985 | 3482 | ZDX | 11/12/2021 | 11/12/2022 | Active |
| 3539 | 8491 | ZIA | 08/28/2022 | 08/28/2023 | Pending Renewal |
| 3476 | 9362 | ZPA | 06/15/2022 | 06/15/2023 | Active |
Write a SQL query to filter the required data from the table.
Answer:
This query filters the data based on Zscaler's interest area. It first checks the status to be 'Active' or 'Pending Renewal'. It then filters the rows based on the service type to be either 'ZIA' or 'ZPA'. Lastly, the query checks for subscriptions that are ending in the next 30 days by determining if the difference between the end date and the current date is less than or equal to 30. This provides a list of customers whose subscription meets the criteria provided and are due for renewal in the next 30 days.
To solve a related SQL problem on DataLemur's free online SQL code editor, try this Meta SQL interview question:
SQL Question 5: When doing database schema design, what's an example of two entities that have a one-to-one relationship? What about one-to-many relationship?
In database schema design, a one-to-one relationship is when each entity is associated with only one instance of the other. For instance, a US citizen's relationship with their social-security number (SSN) is one-to-one because each citizen can only have one SSN, and each SSN belongs to one person.
A one-to-many relationship, on the other hand, is when one entity can be associated with multiple instances of the other entity. An example of this is the relationship between a person and their email addresses - one person can have multiple email addresses, but each email address only belongs to one person.
SQL Question 6: Finding Zscaler Customer Records
Given a table named containing records of customer transactions with Zscaler, you are tasked to find all the records where the column contains 'yahoo'. Assume the table has the following columns: , , , , .
Example Input:
| purchase_id | product_id | user_id | purchase_date | |
|---|---|---|---|---|
| 5012 | 785 | 442 | test@gmail.com | 03/28/2021 |
| 2100 | 546 | 145 | test@yahoo.com | 08/19/2021 |
| 2001 | 217 | 999 | user@yahoo.com | 09/12/2021 |
| 3679 | 689 | 672 | data@yahoo.com | 10/10/2021 |
| 2456 | 897 | 359 | info@gmail.com | 11/20/2021 |
Example Output:
| purchase_id | product_id | user_id | purchase_date | |
|---|---|---|---|---|
| 2100 | 546 | 145 | test@yahoo.com | 08/19/2021 |
| 2001 | 217 | 999 | user@yahoo.com | 09/12/2021 |
| 3679 | 689 | 672 | data@yahoo.com | 10/10/2021 |
Answer:
This query uses the keyword in SQL to filter out the records in the table where the column contains the string 'yahoo'. The percentage sign () on both sides of 'yahoo' is a wildcard character that matches zero or more characters. Therefore, it will return all rows where 'yahoo' appears anywhere in the field.
To solve a similar SQL problem on DataLemur's free interactive coding environment, attempt this SQL interview question asked by Facebook:
SQL Question 7: What's a database view?
Database views are virtual tables based on the results of a SQL statement. They're just like vanilla tables, except views allow you to create simplified versions of tables or hide sensitive data from certain users.
In PostgreSQL, you can create a view by using the command. Here's an example for the table:
SQL Question 8: Calculating Average Monthly Power Usage
Given Zscaler is a global leader in cloud security, they use a large number of servers to manage their workload. Therefore, let's assume you have been provided with a dataset about the total power that the servers have consumed (in kWh) in different departments of the company for each day. Your task is to calculate the average monthly power used by the servers in each department and round it to the nearest integer. Additionally, you need to calculate the percentage difference in power usage between consecutive months.
Example Input:
| date_id | department_id | power_used |
|---|---|---|
| 06/08/2022 | 1 | 500 |
| 06/10/2022 | 1 | 550 |
| 06/15/2022 | 2 | 700 |
| 07/10/2022 | 1 | 450 |
| 07/12/2022 | 2 | 625 |
Example Output:
| mth | department_id | avg_power_used | percentage_diff |
|---|---|---|---|
| 6 | 1 | 525 | NULL |
| 6 | 2 | 700 | NULL |
| 7 | 1 | 450 | -14 |
| 7 | 2 | 625 | -10.7 |
Answer:
This query first calculates the average power used by each department for each month. Then, using the LAG() function, it compares the average power used in the current month to that in the previous month to calculate the percentage difference. Please note that it still may be necessary to deal with NULL values in the column depending on the exact requirements.
To practice a similar problem about calculating rates, try this TikTok SQL question within DataLemur's online SQL code editor:
SQL Question 9: Analyzing Monthly Data Traffic Usage
Zscaler is a global cloud-based information security company. They provide internet security, web security, next generation firewalls, sandboxing, SSL inspection, antivirus, vulnerability management and granular control of user activity in cloud computing, mobile and Internet of things environments.
Suppose you're a data analyst at Zscaler and you're tasked to analyze the monthly data traffic usage of their customers. You have a table named 'traffic' and you want to know the total data traffic that's utilized on a monthly basis for the year 2022.
The 'traffic' table has the following fields:
- id as integer (unique identifier)
- customer_id as integer
- date_time as timestamp
- data_used as float
For the purpose of this question, data_used is measured in Gigabytes (GB).
Example Input:
| id | customer_id | date_time | data_used |
|---|---|---|---|
| 101 | 4356 | 01/05/2022 06:25:00 | 5.0 |
| 102 | 9812 | 01/23/2022 09:42:00 | 3.4 |
| 103 | 4356 | 02/05/2022 12:59:00 | 4.2 |
| 104 | 5021 | 02/18/2022 14:18:00 | 5.0 |
| 105 | 9812 | 02/28/2022 08:25:00 | 3.0 |
Questions:
Find the total data_traffic_used on a monthly basis for year 2022.
Expected output:
| month | total_data_used |
|---|---|
| 1 | 8.4 |
| 2 | 12.2 |
Answer:
Explaination:
This PostgreSQL query extracts the month and year from the field by using EXTRACT function. The WHERE clause filters out the traffic data for the year 2022. Then, the query calculates the sum of for each month of 2022. The result of this query shows the total data traffic used for each month in 2022, which assists in analyzing the monthly data usage. The ROUND function rounds the resultant decimal value to two places.
To solve another question about calculating rates, try this TikTok SQL Interview Question on DataLemur's online SQL code editor:
How To Prepare for the Zscaler SQL Interview
Assuming that you've already got basic SQL skills, the next best tip we have to prepare for the Zscaler SQL interview is to solve as many practice SQL interview questions as you can!
Beyond just solving the earlier Zscaler SQL interview questions, you should also solve the 200+ FAANG SQL Questions on DataLemur which come from companies like Amazon, Microsoft, Meta, and smaller tech companies.
Each DataLemur SQL question has hints to guide you, full answers and most importantly, there is an online SQL coding environment so you can instantly run your query and have it graded.
To prep for the Zscaler SQL interview it is also a great idea to practice SQL problems from other tech companies like:
However, if your SQL query skills are weak, don't worry about jumping right into solving questions – strengthen your SQL foundations with this free SQL tutorial.
This tutorial covers SQL concepts such as LEFT vs. RIGHT JOIN and handling dates – both of these come up routinely in SQL interviews at Zscaler.
Zscaler Data Science Interview Tips
What Do Zscaler Data Science Interviews Cover?
For the Zscaler Data Science Interview, besides SQL questions, the other types of questions to prepare for are:
- Probability & Stats Questions
- Python or R Coding Questions
- Open-Ended Data Case Studies
- ML Modelling Questions
- Behavioral & Resume-Based Questions
How To Prepare for Zscaler Data Science Interviews?
To prepare for Zscaler Data Science interviews read the book Ace the Data Science Interview because it's got:
- 201 interview questions sourced from Microsoft, Amazon & startups
- a refresher covering SQL, AB Testing & ML
- over 900+ 5-star reviews on Amazon