8 Blackbaud SQL Interview Questions (Updated 2024)
At Blackbaud, SQL is often used for extracting and analyzing customer data for nonprofit fundraising strategies. For this reason Blackbaud typically asks SQL questions in interviews for Data Science, Analytics, and & Data Engineering jobs.
As such, to help you study for the Blackbaud SQL interview, this blog covers 8 Blackbaud SQL interview questions – can you answer each one?
8 Blackbaud SQL Interview Questions
SQL Question 1: Retrieve Yearly Fundraising Performance Data
As a data analyst for Blackbaud, a cloud software company powering social good, the manager asks you to analyze the fundraising performance of different causes supported by the charity organizations that use your platform. Specifically, you're asked to write a SQL query that retrieves the total funds raised each year for each cause, from 2018 to 2022, and also calculates the year-over-year growth by comparing the funds raised in the current year with the previous year.
Example Input:
| fundraising_id | cause | year | funds_raised |
|---|---|---|---|
| 4517 | Education | 2018 | 50000 |
| 5293 | Healthcare | 2018 | 60000 |
| 7802 | Education | 2019 | 80000 |
| 6352 | Healthcare | 2019 | 90000 |
| 6171 | Education | 2020 | 100000 |
| 8956 | Healthcare | 2020 | 120000 |
| 9734 | Education | 2021 | 150000 |
| 5274 | Healthcare | 2021 | 200000 |
| 2631 | Education | 2022 | 220000 |
| 8316 | Healthcare | 2022 | 300000 |
Answer:
This PostgreSQL query starts by creating a aggregated table which calculates the total funds raised for each cause each year. It then creates a table which includes a new column that's calculated by the function, creating a time lag for the variable per each .
The final SELECT query then calculates and returns the year-over-year growth rate for each cause, taking into account for the fact that the funds raised in the previous year can be 0 (to avoid division by zero errors, the null value would be returned for the growth in the first year because there isn't a previous year of data available for comparison). The results pulled by this query allows the company to see the fundraising performance of each cause over time and how it has changed on a yearly basis.
To practice another window function question on DataLemur's free online SQL code editor, try this Amazon SQL question asked in a BI Engineer interview:
SQL Question 2: Average Donation Amount
As a database analyst for Blackbaud, a cloud computing provider specializing in nonprofit software, you are tasked with determining the average donation amount made by donors on a monthly basis, in the year 2022.
Example Input:
| donation_id | donor_id | donation_date | amount |
|---|---|---|---|
| 1024 | 5678 | 01/08/2022 | 50 |
| 1025 | 9101 | 01/15/2022 | 20 |
| 1026 | 1213 | 02/04/2022 | 35 |
| 1027 | 1415 | 03/18/2022 | 70 |
| 1028 | 5678 | 03/25/2022 | 25 |
Example Output:
| month | avg_amount |
|---|---|
| 1 | 35 |
| 2 | 35 |
| 3 | 47.5 |
Answer:
This SQL query first extracts the month from the donation dates, then groups the records by month and calculates the average donation amount for each month. The WHERE condition is used to filter the results for the year 2022. The results are ordered by month in ascending order.
To practice a very similar question try this interactive Facebook Active User Retention Question which is similar for analyzing monthly user engagement or this Amazon Average Review Ratings Question which is similar for calculating average amounts on a monthly basis.
SQL Question 3: Could you explain what a self-join is?
A self-join is a operation in which a single table is joined to itself. To perform a self-join, you must specify the table name twice in the clause, giving each instance a different alias. You can then join the two instances of the table using a clause, and specify the relationship between the rows in a clause.
Think of using a self-joins whenever your data analysis involves analyzie pairs of the same things, like comparing the salaries of employees within the same department, or identifying pairs of products that are frequently purchased together (which you can do in this real SQL question from a Walmart interview).
For another self-join example, suppose you were conducting an HR analytics project and needed to examine how frequently employees within the same department at Blackbaud interact with one another, you could use a self-join query like the following to retrieve all pairs of Blackbaud employees who work in the same department:
This query returns all pairs of Blackbaud employees who work in the same department, and excludes pairs where the employee's id is the same (since this would represent the same Blackbaud employee being paired with themselves).
SQL Question 4: Average Donation Amount by Fund Category
As a software engineer at Blackbaud, a company that offers software solutions for fundraising and relationship management, you are tasked to help their client, a non-profit organization, gain insights into their donations. They specifically want to know the average donation amount they receive under each fund category in the year 2022.
Example Input:
| donation_id | donor_id | donation_date | fund_category | donation_amount |
|---|---|---|---|---|
| 7891 | 541 | 01/15/2022 | Education | $50 |
| 4562 | 214 | 02/20/2022 | Healthcare | $100 |
| 3227 | 279 | 03/30/2022 | Education | $75 |
| 8475 | 416 | 04/04/2022 | Art & Culture | $150 |
| 1649 | 985 | 05/25/2022 | Healthcare | $50 |
Answer:
This query calculates the average donation amount for each fund category on a monthly basis in the year 2022. This is first done by filtering out the donations from the year 2022, then grouping by the month and fund category, and finally calculating the average donation amount in each group. The result is sorted by the month and fund category.
Example Output:
| month | fund_category | average_donation |
|---|---|---|
| 1 | Education | $50.00 |
| 2 | Healthcare | $100.00 |
| 3 | Education | $75.00 |
| 4 | Art & Culture | $150.00 |
| 5 | Healthcare | $50.00 |
SQL Question 5: How do foreign and primary keys differ?
To explain the difference between a primary key and foreign key, let's start with some data from Blackbaud's marketing analytics database which stores data from Google Ads campaigns:
:
+------------+------------+------------+------------+ | ad_id | campaign_id| keyword | click_count| +------------+------------+------------+------------+ | 1 | 100 | Blackbaud pricing | 10 | | 2 | 100 | Blackbaud reviews | 15 | | 3 | 101 | Blackbaud alternatives | 7 | | 4 | 101 | buy Blackbaud | 12 | +------------+------------+------------+------------+
In this table, could be a primary key. It is unique for each row in the table and cannot contain null values.
could be a foreign key. It references the of the Google Ads campaign that each ad belongs to, establishing a relationship between the ads and their campaigns. This foreign key allows you to easily query the table to find out which ads belong to a specific campaign, or to find out which campaigns a specific ad belongs to.
It is also possible for a table to have multiple foreign keys that reference different primary keys in other tables. For example, the table could have additional foreign keys for the of the ad group that each ad belongs to, and the of the Google Ads account that the campaigns belong to.
SQL Question 6: Joining a Customer and Transactions Database
A company named "Blackbaud" has two databases - one for customers and another for transactions. Each row in the customers table represents a unique customer, and each row in the transactions table represents a unique transaction carried out by the customers.
-
The database has columns , , , , and .
-
The database has columns , , , and .
Write a SQL query to join the two tables to create an overview that includes customer details, transaction product id, transaction date and product price. The resulting data should be sorted by transaction date in descending order.
Example Input:
| customer_id | first_name | last_name | city | state | |
|---|---|---|---|---|---|
| 1001 | John | Doe | john.doe@email.com | New York | NY |
| 1002 | Jane | Smith | jane.smith@email.com | San Francisco | CA |
| 1003 | Bob | Johnson | bob.johnson@email.com | Austin | TX |
| 1004 | Alice | Williams | alice.williams@email.com | Seattle | WA |
Example Input:
| transaction_id | customer_id | product_id | transaction_date | product_price |
|---|---|---|---|---|
| 5678 | 1001 | 2001 | 2022-06-10 | 350 |
| 8970 | 1002 | 2002 | 2022-05-15 | 500 |
| 7896 | 1001 | 2003 | 2022-07-01 | 150 |
| 8907 | 1004 | 2001 | 2022-06-20 | 350 |
Answer:
This query will give a joint view of the two tables where each row contains customer personal details, the product id of a transaction made by the customer, the date of the transaction and the price of the product purchased, sorted by the date of the transaction in descending order. This can be helpful in understanding the activity of the customers.
Since join questions come up routinely during SQL interviews, take a stab at this SQL join question from Spotify:
SQL Question 7: How do and differ when it comes to ranking rows in a result set?
As the name implies, the window function ranks each row within your window/partition. If two rows have the same rank, the next number in the ranking will be the previous rank plus the number of duplicates. For example, if you've got three records tied for 5th place, they'll get the values 5, 6, and 7, and the next row after this 3-way tie will have a rank of 8.
The function assigns a distinct rank to each row within a partition based on the provided column value with no gaps. This function will assign the same rank to two rows if they have the same rank, and give the next row the next rank number. To make this more concrete, imagine you had three records at rank 5 – then, the next rank would be 6.
SQL Question 8: Statistical Summary of Donor Gift Amounts
Blackbaud is a cloud software company specializing in software for nonprofits. Their systems frequently manage private donor data, gift amounts, and the dates those gifts were given. A common request from their clients would be statistical summaries of their donors and gift amounts.
It's your job to compile a statistical summary of the table for each . You should calculate the mean (), standard deviation (), and round both results to 2 decimal places.
Example Input:
| gift_id | donor_id | amount | gift_date |
|---|---|---|---|
| 1 | 1 | 25.00 | 2021-05-18 |
| 2 | 1 | 50.00 | 2021-04-10 |
| 3 | 2 | 60.00 | 2021-06-11 |
| 4 | 2 | 80.00 | 2021-03-09 |
| 5 | 2 | 100.00 | 2021-09-19 |
SQL Query:
Example Output:
| donor_id | mean_gift_amount | stddev_gift_amount |
|---|---|---|
| 1 | 37.50 | 17.68 |
| 2 | 80.00 | 20.00 |
This solution groups all rows by , then uses the aggregate function and , rounding to 2 decimal places with the function.
To practice a very similar question try this interactive Alibaba Compressed Mean Question which is similar for calculating the mean or this Amazon Average Review Ratings Question which is similar for performing data aggregation per user.
How To Prepare for the Blackbaud SQL Interview
Assuming that you've already got basic SQL skills, the next best tip we have to prepare for the Blackbaud SQL interview is to solve as many practice SQL interview questions as you can!
Besides solving the above Blackbaud SQL interview questions, you should also solve the 200+ SQL questions from real Data Science & Analytics interviews which come from companies like Facebook, Google and unicorn tech startups.
Each interview question has hints to guide you, step-by-step solutions and crucially, there's an online SQL coding environment so you can easily right in the browser your SQL query and have it executed.
To prep for the Blackbaud SQL interview you can also be wise to practice SQL problems from other tech companies like:
In case your SQL query skills are weak, forget about going right into solving questions – improve your SQL foundations with this SQL tutorial for Data Analytics.
This tutorial covers SQL topics like sorting results with ORDER BY and aggregate functions – both of which come up frequently during Blackbaud interviews.
Blackbaud Data Science Interview Tips
What Do Blackbaud Data Science Interviews Cover?
In addition to SQL query questions, the other topics to practice for the Blackbaud Data Science Interview are:
- Statistics & Probability Questions
- Python or R Coding Questions
- Data Case Study Questions
- ML Modelling Questions
- Behavioral Based Interview Questions
How To Prepare for Blackbaud Data Science Interviews?
The best way to prepare for Blackbaud Data Science interviews is by reading Ace the Data Science Interview. The book's got:
- 201 Interview Questions from Facebook, Google, & Amazon
- A Crash Course on Stats, SQL & ML
- Amazing Reviews (900+ reviews, 4.5-star rating)