SQL case study questions go beyond basic SQL queries, presenting hypothetical business scenarios that require you to define relevant metrics and write queries to investigate problems. These questions test your analytical thinking and SQL skills simultaneously.
To excel in SQL case study interviews, practice walking through solutions step-by-step. This approach helps you:
Let’s explore two comprehensive SQL case study examples with detailed solutions.
Scenario: Twitter implemented a new notification system in an A/B test, resulting in increased unsubscribe rates.
Available Data:
events
table (user_id, created_at, action)variants
table (user_id, experiment, variant)Goal: Create a query to visualize how unsubscribes affect login rates over time.
1. Make Assumptions
2. Develop a Hypothesis
3. SQL Implementation
SELECT
variant,
DATEDIFF(e1.created_at, e2.created_at) AS days_since_unsub,
ROUND(COUNT(DISTINCT CASE WHEN e2.action = 'login'
THEN 1 ELSE 0 END)/COUNT(DISTINCT abtest.user_id) * 100, 2) AS login_rate
FROM variants as abtest
INNER JOIN events AS e1
ON abtest.user_id = e1.user_id
AND e1.action = 'unsubscribe'
INNER JOIN events AS e2
ON abtest.user_id = e2.user_id
AND e2.action IN ('login', 'nologin')
AND DATEDIFF(e1.created_at, e2.created_at)
BETWEEN -30 AND 30
GROUP BY 1,2
This course is designed to help you learn everything you need to know about working with data, from basic concepts to more advanced techniques.
If you have an interview coming up, review Interview Query’s data science course, which includes modules in SQL.
SQL interviews are demanding, and the more you practice all types of SQL interview questions and not just case questions, the more confident and efficient you’ll become in answering them.
Scenario: Analyzing career paths of data scientists to determine if frequent job changes lead to faster promotion to management roles.
Available Data:
user_experiences
table (id, user_id, title, company, start_date, end_date, is_current_role)Goal: Prove or disprove the hypothesis that data scientists who switch jobs more often get promoted to management faster.
1. Make Assumptions
2. Develop a Hypothesis
3. SQL Implementation
WITH manager_promo as (
SELECT user_id,
MIN(start_date) as promotion_date
FROM playground.user_experiences
WHERE title='data science manager'
GROUP BY user_id
)
SELECT num_jobs_switched,
AVG(
TIMESTAMPDIFF(MONTH, career_started_date, promotion_date)
) as month_to_promo
FROM (
SELECT u.user_id,
mp.promotion_date,
COUNT(DISTINCT u.id) as num_jobs_switched,
MIN(start_date) as career_started_date
FROM playground.user_experiences u
INNER JOIN manager_promo mp
on u.user_id=mp.user_id
WHERE u.start_date<mp.promotion_date
GROUP BY u.user_id, mp.promotion_date
) tt
GROUP BY num_jobs_switched
ORDER BY 2 DESC
4. Analysis Considerations
Mastering SQL case studies requires both technical SQL skills and business acumen to translate hypothetical scenarios into actionable insights.