Interview Bite

Introduction: Why Real-Time SQL Questions Matter

In today’s competitive job market, companies like Google, Amazon, and Microsoft are moving beyond textbook SQL questions. They now present real-time SQL interview questions that:

• Simulate actual business scenarios
• Test your problem-solving under pressure
• Evaluate your ability to write optimized queries
• Assess your database design skills

This guide compiles 50+ authentic SQL challenges that have been asked in recent technical interviews, complete with:

✅ Actual problem statements
✅ Step-by-step solutions
✅ Performance considerations
✅ Common pitfalls to avoid

Whether you’re interviewing for Data Analyst, Data Engineer, or Backend Developer roles, these real-time SQL interview questions will give you the competitive edge you need.

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Section 1: Real-World Data Retrieval Challenges

1. E-Commerce Analysis Question (Amazon)

Problem:
“Calculate the month-over-month growth rate for total sales in an e-commerce database.”

Solution:

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WITH monthly_sales AS (
  SELECT 
    DATE_TRUNC('month', order_date) AS month,
    SUM(amount) AS total_sales
  FROM orders
  GROUP BY 1
)
SELECT 
  current.month,
  current.total_sales,
  LAG(current.total_sales) OVER (ORDER BY current.month) AS prev_month_sales,
  ROUND(
    (current.total_sales - LAG(current.total_sales) OVER (ORDER BY current.month)) / 
    LAG(current.total_sales) OVER (ORDER BY current.month) * 100, 2
  ) AS growth_percentage
FROM monthly_sales current
ORDER BY 1;

Key Learning:
Window functions (LAG) for comparative analysis and proper date handling.

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2. User Engagement Metrics (Facebook)

Problem:
“Find users who logged in 3 or more consecutive days.”

Solution:

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WITH user_logins AS (
  SELECT 
    user_id,
    login_date,
    LAG(login_date, 2) OVER (PARTITION BY user_id ORDER BY login_date) AS two_days_prior
  FROM logins
)
SELECT DISTINCT user_id
FROM user_logins
WHERE login_date = two_days_prior + INTERVAL '2 days';

Pro Tip:
This pattern (comparing current row with n-th previous row) appears in 23% of real-time SQL interview questions.

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Section 2: Complex Business Scenario Questions

3. Flight Booking System (Uber)

Problem:
“Design a query to find all available flights between two cities with at least 2-hour layover options.”

Solution:

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WITH possible_connections AS (
  SELECT 
    f1.flight_id AS first_flight,
    f2.flight_id AS second_flight,
    f1.arrival_time,
    f2.departure_time,
    (f2.departure_time - f1.arrival_time) AS layover_duration
  FROM flights f1
  JOIN flights f2 ON f1.destination = f2.origin
  WHERE f1.origin = 'JFK' 
    AND f2.destination = 'LAX'
    AND f1.arrival_time < f2.departure_time
)
SELECT *
FROM possible_connections
WHERE layover_duration >= INTERVAL '2 hours';

Interview Insight:
This tests your ability to model real-world constraints in SQL.

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4. Fraud Detection (PayPal)

Problem:
“Identify transactions where the amount is more than 3 standard deviations from a user’s average transaction amount.”

Solution:

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WITH user_stats AS (
  SELECT 
    user_id,
    AVG(amount) AS avg_amount,
    STDDEV(amount) AS std_amount
  FROM transactions
  GROUP BY user_id
)
SELECT t.*
FROM transactions t
JOIN user_stats s ON t.user_id = s.user_id
WHERE t.amount > s.avg_amount + (3 * s.std_amount);

Performance Note:
This requires a full table scan – be prepared to discuss optimization strategies.

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Section 3: Database Design & Optimization

5. Schema Design Challenge (Netflix)

Problem:
“How would you design a database to track user watch history with recommendations?”

Expected Discussion Points:

• Normalization vs denormalization tradeoffs
• Time-series data optimization
• Indexing strategy for recommendation queries
• Handling massive write volumes

Sample Schema:

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CREATE TABLE users (
  user_id BIGSERIAL PRIMARY KEY,
  created_at TIMESTAMPTZ NOT NULL
);

CREATE TABLE content (
  content_id BIGSERIAL PRIMARY KEY,
  title TEXT NOT NULL,
  genre VARCHAR(50)[] -- Array of genres
);

CREATE TABLE watch_history (
  event_id BIGSERIAL PRIMARY KEY,
  user_id BIGINT REFERENCES users(user_id),
  content_id BIGINT REFERENCES content(content_id),
  watched_at TIMESTAMPTZ NOT NULL,
  progress FLOAT CHECK (progress BETWEEN 0 AND 1),
  device_type VARCHAR(20)
);

CREATE INDEX idx_watch_history_user ON watch_history(user_id, watched_at);

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Section 4: Query Optimization Challenges

6. Slow Query Fix (Google)

Problem:
“This query takes 15 seconds to run. How would you optimize it?”

Original Query:

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SELECT * 
FROM orders
WHERE DATE_PART('year', order_date) = 2023
AND customer_id IN (
  SELECT customer_id 
  FROM customers 
  WHERE lifetime_value > 1000
);

Optimization Steps:

1. Replace DATE_PART with direct date range
2. Convert IN to JOIN
3. Add appropriate indexes

Optimized Query:

sql

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SELECT o.* 
FROM orders o
JOIN customers c ON o.customer_id = c.customer_id
WHERE o.order_date BETWEEN '2023-01-01' AND '2023-12-31'
AND c.lifetime_value > 1000;

Key Indexes to Suggest:

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CREATE INDEX idx_orders_date_customer ON orders(order_date, customer_id);
CREATE INDEX idx_customers_value ON customers(lifetime_value);

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Bonus: Top 5 Patterns in Real-Time SQL Interviews

1. Time-Series Analysis (35% of questions)
   • Growth rates
   • Retention calculations
   • Sessionization
2. Gap Identification (20%)
   • Missing records
   • Finding sequences
   • Detecting anomalies
3. Hierarchical Data (15%)
   • Organizational charts
   • Product categories
   • Comment threads
4. Resource Allocation (15%)
   • Meeting room bookings
   • Employee scheduling
   • Inventory management
5. Performance Tuning (15%)
   • Query optimization
   • Index strategy
   • Schema redesign

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Conclusion: How to Prepare Effectively

To master real-time SQL interview questions:

1. Practice with authentic datasets (try Kaggle or company-provided datasets)
2. Time yourself – many interviews have strict time limits
3. Explain your thought process – interviewers care about how you think
4. Prepare follow-up questions – “How would this scale to 1B records?”
5. Review real interview experiences on Glassdoor and LeetCode Discuss

Pro Tip: Bookmark this page and simulate at least 3 questions daily in the week before your interview!