In October 2019, my friend Wayne was stuck in a dead-end job.
He felt like he had a lot of skills to offer, but couldn’t get a chance. He had an eye for data and I suggested he check out some data analytics jobs. Things clicked and he dove right in.
Then impostor syndrome took over.
His heart pounded before every job interview. The fear of being “found out” as a fraud left him drenched in cold sweats. How was he supposed to compete with other candidates who seemed to have mastered SQL when he felt like a total beginner?
Wayne grappled with endless what-ifs:
- What if he couldn’t recall the syntax during an interview?
- What if he couldn’t solve a complex SQL problem under time pressure?
- What if his SQL knowledge was simply not good enough?
The impostor syndrome amplified his doubts. It grew into a beast, casting long shadows over his confidence. It was severely crippling.
It was so overwhelming that Wayne almost considered giving up on his dream data analytics career.
Then, a lightbulb went off. Wayne realized that practice was the key to taming the beast of impostor syndrome.
So, he got to work.
With a newfound resolve, Wayne started practicing SQL problems. He tackled beginner, intermediate, and advanced levels. No problem was too small or too challenging.
As he went through this rigorous routine, something incredible happened.
Gradually, he found his fear retreating. His SQL knowledge was growing, and with it, so was his confidence. Every problem solved, every query executed perfectly, was a hammer blow to his self-doubt.
Wayne transformed his future. One SQL problem at a time.
Fast forward a few months, and Wayne walked into job interviews with a cool composure. The SQL beast that once made his palms sweat was now his trusted ally.
No more fear of being found out. No more sleepless nights before an interview. No more crippling self-doubt.
Instead, he viewed every SQL question as an opportunity:
- To showcase his skills.
- To land the job of his dreams.
- To stand out from the competition.
And you know what? He did just that.
With the right amount of practice and dedication, you too can overcome impostor syndrome in your data analytics career.
If SQL problems are your beast, then it’s time to tame it. Practice consistently. Start from the beginner level, make your way up to the intermediate, and then challenge yourself with the advanced.
Remember, every problem solved is a step closer to a brighter, more confident future.
Because in the end, you’re not an impostor.
You’re a data analyst in the making.
This guide includes marketing problems that data analysts face in the real world all the time.
And companies across the globe pay experts thousands of dollars each day just to solve them. I believe that you can be that expert. And practice interview questions like these are the ticket to your success.
How this guide works:
- Use the database diagram below to write the SQL that answers each question
- The questions get more difficult and are based on real-world business problems.
- If you get stuck, all of the SQL code you need can be found here.
- I’ve also listed all of the answers below. But try it on your own first!
Use this database diagram to answer the questions.
 |
Questions
Question 1: Customers by Channel (Beginner)
Can you write a SQL query to count the number of customers acquired through each acquisition channel?
This one is straightforward – just count the number of customers per acquisition channel.
Use a GROUP BY clause to group the customers by their acquisition channel and the COUNT(*) function counts the number of rows (i.e., customers) in each group.
Try it on your own and then check your answers against the online SQL code found here.
Question 2: Order Value by Channel (Intermediate)
Can you write a SQL query to find the total order value for each acquisition channel?
You’ll need to first join the Customers, Orders, and MarketingChannels tables using the appropriate foreign keys.
Then group the resulting data by the acquisition channel and sum the order value for each group.
The WHERE clause ensures we only consider orders that were made through the same channel as the customer’s acquisition channel.
Try it on your own and then check your answers against the online SQL code found here.
Question 3: Top Customers by Channel Sales (Advanced)
Can you write a SQL query to calculate the total order value for each customer’s orders, partitioned by acquisition channel, and then rank them based on the total order value within each channel? This should be performed using CTEs and window functions. Include only the top 3 customers by channel.
This query is more complex and requires Common Table Expressions (CTEs).
Try it on your own and then check your answers against the online SQL code found here.
Answers
Answer 1: Customers by Channel (Beginner)
Here’s my SQL. View the online version here.
-- Question 1: Beginner Level -- How many customers were acquired through each channel? SELECT AcquisitionChannel, COUNT(*) as NumberOfCustomers FROM Customers GROUP BY AcquisitionChannel;
Step by step
- Familiarize yourself with the GROUP BY clause. It allows you to separate data into groups, which can be aggregated independently.
- The COUNT() function is used to count the number of rows in each group. Be sure you understand how to use it properly.
- Understanding the table structure and column details is crucial. In this question, you need to understand that AcquisitionChannel is a column in the Customers table.
Answer 1 Results
| acquisitionchannel | numberofcustomers |
|---|---|
| 21 | |
| Social Media | 19 |
Answer 2: Order Value by Channel (Intermediate)
Here’s my SQL. View the online version here.
-- Question 2: Intermediate Level -- What's the total value for each channel? SELECT c.AcquisitionChannel, SUM(o.OrderValue) as TotalOrderValue FROM Customers c JOIN Orders o ON c.CustomerID = o.CustomerID JOIN MarketingChannels mc ON o.OrderID = mc.OrderID WHERE c.AcquisitionChannel = mc.ChannelName GROUP BY c.AcquisitionChannel;
Step by step
- This question requires a clear understanding of SQL JOINs to merge rows from multiple tables. In this case, you are joining the Customers, Orders, and MarketingChannels tables.
- The SUM() function is used to get the total order value. Be comfortable with using this function over specific columns.
- The WHERE clause is utilized to filter out the records where the order was made through the same channel as the customer’s acquisition channel. This adds an extra layer of complexity to the question.
Answer 2 Results
| acquisition_channel | total_order_value |
|---|---|
| 6500.00 | |
| Social Media | 5000.00 |
Answer 3: Top Customers by Channel Sales (Advanced)
Here’s my SQL. View the online version here.
-- Question 3: Advanced Level
-- Customer Sales Ranking by Channel
WITH CustomerOrders AS (
SELECT
c.CustomerID,
c.AcquisitionChannel,
SUM(o.OrderValue) AS TotalOrderValue
FROM Customers c
JOIN Orders o ON c.CustomerID = o.CustomerID
GROUP BY c.CustomerID, c.AcquisitionChannel
),
RankedOrders AS (
SELECT
CustomerID,
AcquisitionChannel,
TotalOrderValue,
RANK() OVER (PARTITION BY AcquisitionChannel ORDER BY TotalOrderValue DESC) AS Rank
FROM CustomerOrders
)
SELECT * FROM RankedOrders WHERE Rank <= 3;
Step by step
- This question requires the use of Common Table Expressions (CTEs). Make sure you understand how to declare and use CTEs in your SQL code.
- Understanding window functions is crucial. Here, the RANK() function is used to rank customers within each acquisition channel based on their total order value.
- It’s important to remember to filter the final results using a WHERE clause to ensure that only the top 3 customers for each acquisition channel are included in the result set.
Answer 3 Results
| customerid | acquisitionchannel | totalordervalue | rank |
|---|---|---|---|
| 19 | 3000.00 | 1 | |
| 18 | 2900.00 | 2 | |
| 16 | 2700.00 | 3 | |
| 20 | Social Media | 3100.00 | 1 |
| 17 | Social Media | 2800.00 | 2 |
| 15 | Social Media | 2600.00 | 3 |
Practicing SQL consistently can turn your fear into your strength, just like Wayne.
Takeaways:
- SQL practice is the ultimate weapon against impostor syndrome.
- Tackling SQL problems at all levels builds confidence and skills.
- You can shift from interview fear to confidence – just like my friend Wayne.
- Each SQL problem you solve is a step closer to confidence and success!
So, what SQL problem are you going to tackle next?