8 Coinbase SQL Interview Questions (Updated 2024)
At Coinbase, SQL is used often for analyzing cryptocurrency transaction patterns and for managing user profile data in the digital wallet. That's why Coinbase frequently asks SQL query questions in interviews for Data Science, Analytics, and & Data Engineering jobs.
So, to help you study for the Coinbase SQL interview, we've curated 8 Coinbase SQL interview questions – able to answer them all?
8 Coinbase SQL Interview Questions
SQL Question 1: Identifying Active Cryptocurrency Buyers
Coinbase, a platform for buying and selling cryptocurrency, wants to identify its most active users - the buyers who make the most transactions. These "whale" users are extremely valuable to the business and need to be recognized and prioritized.
Our task is to write a SQL query that will find the top 10 users who have made the most cryptocurrency purchases within the last month.
Example Input:
Example Output:
Answer:
This query first creates a subquery that groups transactions by user id, and counts the number of transactions made by each user within the current month. The main query then sorts the users by the count of their transactions in descending order and retrieves the top 10 users.
To practice a similar customer analytics SQL question where you can code right in the browser and have your SQL query instantly graded, try this Walmart Labs SQL Interview Question:
SQL Question 2: Analyze Daily Cryptocurrency Trading Volume for Coinbase Users
As a data analyst for Coinbase, one of your tasks is to analyze the trading volume of different cryptocurrencies.
You have been given a transaction table where each row represents a completed trade by Coinbase users. Each-trade has an associated , - representing the type of cryptocurrency that was traded, and - representing the quantity of cryptocurrency that was traded in that transaction.
The task is to write a SQL query that returns the daily trading volume of each cryptocurrency, additionally return the difference between the current day's volume and the previous day's volume for each currency.
Please refer below for an example of table:
Example Input:
| trade_id | user_id | currency_id | trade_date | volume |
|---|---|---|---|---|
| 1 | 100 | 39 | 2022-07-01 | 2.0 |
| 2 | 101 | 12 | 2022-07-01 | 3.5 |
| 3 | 103 | 39 | 2022-07-02 | 1.5 |
| 4 | 105 | 12 | 2022-07-02 | 4.0 |
| 5 | 100 | 39 | 2022-07-02 | 2.0 |
| 6 | 103 | 12 | 2022-07-03 | 1.5 |
Note: Assume all volumes are in same measure, say "Bitcoin".
Example Output:
| trade_date | currency_id | total_volume | volume_difference |
|---|---|---|---|
| 2022-07-01 | 39 | 2.0 | NA |
| 2022-07-01 | 12 | 3.5 | NA |
| 2022-07-02 | 39 | 3.5 | 1.5 |
| 2022-07-02 | 12 | 4.0 | 0.5 |
| 2022-07-03 | 12 | 1.5 | -2.5 |
Answer:
We can solve this using SQL window function . This function provides access to a row at a specified physical offset that comes before the current row.
Here is the SQL query for the problem:
In this query, the function is used to get the previous day's total_volume. The calculates the total volume for each date and currency_id. Then we subtract the previous day's volume from the current day's volume to get the volume difference. The final result is ordered by trade_date and currency_id.
p.s. Window functions show up super frequently during SQL interviews, so practice the 27+ window function questions on DataLemur
SQL Question 3: Can you explain the meaning of database denormalization?
Database denormalization is when you add redundancy to a database, and break typical normalization rules (codified by the 1st, 2nd, 3rd normal forms).
Denormalization is typically used to improve the performance of a database, particularly when the database is being for OLAP (Online Analytical Processing) purposes. By denormalizing a database, you can reduce the number of joins that are required to retrieve data, which can greatly improve the speed of queries since joins are costly and slow. However, denormalization can also introduce some problems, such as increased data redundancy and the need for more complex update and delete operations since data has been duplicated into multiple tables.
In general, denormalization should be used with caution and only after careful consideration of the trade-offs involved. It's typically better to start with a well-normalized database design then denormalize only if your database isn't scaling as well as you want.
SQL Question 4: Find the Average Transaction Amount for Different Cryptocurrencies
In the context of Coinbase, a cryptocurrency trading platform, you could be given the task to calculate the average transaction amount for different cryptocurrencies such as Bitcoin (BTC), Ethereum (ETH), etc., from a table. The table might look something like this:
Example Input:
| transaction_id | user_id | transaction_date | currency | amount |
|---|---|---|---|---|
| 1001 | 456 | 06/08/2022 00:00:00 | BTC | 0.01 |
| 1002 | 789 | 06/09/2022 00:00:00 | ETH | 2 |
| 1003 | 123 | 06/10/2022 00:00:00 | BTC | 0.02 |
| 1004 | 321 | 07/26/2022 00:00:00 | LTC | 5 |
| 1005 | 654 | 07/05/2022 00:00:00 | ETH | 3 |
The task will be to write a PostgreSQL statement to calculate the average transaction amount for each kind of cryptocurrency. The output should resemble:
Example Output:
| currency | avg_amount |
|---|---|
| BTC | 0.015 |
| ETH | 2.50 |
| LTC | 5.00 |
Answer:
This SQL query above uses the function to calculate the average transaction amount grouped by each type of cryptocurrency. By including the in the clause, it calculates the average for each distinct currency in the transactions table. The clause is used here to rename the second column of the result set as "avg_amount" for better readability.
To practice a very similar question try this interactive Uber User's Third Transaction Question which is similar for involving transaction data or this Stripe Repeated Payments Question which is similar for needing to analyze payment behaviour.
SQL Question 5: What does the SQL command do?
When using , only rows that are identical in both sets will be returned.
For a concrete example, say you were a Data Analyst supporting the Sales Analytics team at Coinbase, and data on potential sales leads lived in both Salesforce and Hubspot CRMs. To write a query to analyze leads created before 2023 started, that show up in BOTH CRMs, you would use the command:
SQL Question 6: Search for Customer Transactions with Specific Cryptocurrency
As a financial analyst at Coinbase, you are tasked with finding all customer transactions that involve a specific cryptocurrency. For this purpose, you have access to the table containing all the transaction details of customers. The table has the columns , , , , and .
Your task is to write a SQL query that finds all transactions where the column has a value that starts with 'BTC'.
Example Input:
| transaction_id | customer_id | transaction_date | crypto_symbol | amount |
|---|---|---|---|---|
| 1 | 123 | 2022-01-01 | BTC | 0.01 |
| 2 | 456 | 2022-01-02 | ETH | 2.5 |
| 3 | 789 | 2022-01-03 | BTC | 1.0 |
| 4 | 123 | 2022-01-04 | DOGE | 1000.0 |
| 5 | 789 | 2022-01-05 | BTC | 0.5 |
Example Output:
| transaction_id | customer_id | transaction_date | crypto_symbol | amount |
|---|---|---|---|---|
| 1 | 123 | 2022-01-01 | BTC | 0.01 |
| 3 | 789 | 2022-01-03 | BTC | 1.0 |
| 5 | 789 | 2022-01-05 | BTC | 0.5 |
Answer:
This query will return all rows from the table where the column starts with 'BTC'. The '%' symbol is a wildcard character in SQL that matches any sequence of characters, so 'BTC%' will match any string that starts with 'BTC'.
SQL Question 7: What is a database index, and what are the different types of indexes?
A database index is a way to optimize the performance of a database by reducing the amount of data that needs to be searched to retrieve a record.
There are several types of indexes that can be used in a database:
- Primary index: a unique identifier is used to access the row directly.
- Unique index: used to enforce the uniqueness of the indexed columns in a table.
- Composite index: created on multiple columns of a table, is used to speed up the search process for multiple columns
- Clustered index: determines the physical order of the data in a table
For a concrete example, say you had a table of Coinbase customer payments with the following columns: payment_id, customer_id, payment_amount, and payment_date.
Here's what a clustered index on the column would look like:
A clustered index on the column would determine the physical order of the records in the table based on the . This means that the records with the earliest values would be stored together physically in the table, followed by records with later payment_date values.
Having a clustered index on the column can speed up queries that filter or sort the data based on the payment_date, as the records are already physically sorted in the table. For example, if you want to retrieve all the payments made in the month of January, the database can use the clustered index to quickly locate and retrieve the desired records without having to search through the entire table.
SQL Question 8: Analyzing Customer Activities on Coinbase
Imagine you're the Data Analyst at Coinbase. The company has two tables, and .
The table includes customer details, like , , and .
The table keeps a log of all cryptocurrency transactions. Its columns include , , , , and .
Example Input:
| customer_id | registration_date | country |
|---|---|---|
| 1204 | 2018-01-03 00:00:00 | USA |
| 1894 | 2019-06-22 00:00:00 | UK |
| 2151 | 2016-09-12 00:00:00 | Canada |
| 3012 | 2020-02-18 00:00:00 | Australia |
| 4518 | 2021-04-10 00:00:00 | USA |
Example Input:
| transaction_id | customer_id | coin_type | transaction_volume | transaction_date |
|---|---|---|---|---|
| 9125 | 1204 | Bitcoin | 2.4 | 2022-06-20 00:00:00 |
| 6541 | 1894 | Etherium | 5.6 | 2022-06-22 00:00:00 |
| 7002 | 2151 | Bitcoin | 3.1 | 2022-06-30 00:00:00 |
| 8552 | 3012 | Etherium | 1.2 | 2022-07-12 00:00:00 |
| 9217 | 4518 | Bitcoin | 4.5 | 2022-07-22 00:00:00 |
Can you write a SQL query to find out the total Bitcoin transaction volume for each country for June 2022?
Answer:
This query joins the table with the table on . The clause then filters the combined data for Bitcoin transactions in June 2022. The clause groups the remaining records by country, and the function is used to calculate the total Bitcoin transaction volume for each country.
Since joins come up frequently during SQL interviews, try this interactive Snapchat SQL Interview question using JOINS:
Coinbase SQL Interview Tips
The key to acing a Coinbase SQL interview is to practice, practice, and then practice some more!
Besides solving the earlier Coinbase SQL interview questions, you should also solve the 200+ tricky sql questions on DataLemur which come from companies like Amazon, Microsoft, Meta, and smaller tech companies.
Each interview question has hints to guide you, full answers and most importantly, there's an online SQL code editor so you can easily right in the browser your SQL query and have it checked.
To prep for the Coinbase SQL interview it is also useful to solve SQL questions from other fintech and crypto companies like:
In case your SQL coding skills are weak, forget about jumping right into solving questions – strengthen your SQL foundations with this SQL tutorial for Data Scientists & Analysts.
This tutorial covers topics including manipulating string/text data and filtering data with WHERE – both of these show up often during SQL interviews at Coinbase.
Coinbase Data Science Interview Tips
What Do Coinbase Data Science Interviews Cover?
In addition to SQL interview questions, the other question categories to practice for the Coinbase Data Science Interview are:
- Statistics & Probability Questions
- Python or R Programming Questions
- Analytics and Product-Metrics Questions
- Machine Learning and Predictive Modeling Questions
- Behavioral & Resume-Based Questions
How To Prepare for Coinbase Data Science Interviews?
The best way to prepare for Coinbase Data Science interviews is by reading Ace the Data Science Interview. The book's got:
- 201 Interview Questions from Facebook, Google & startups
- A Crash Course on Python, SQL & ML
- Great Reviews (900+ reviews, 4.5-star rating)
They also have a unique culture, so definitely study-up on the Coinbase mission & values!