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We use INNER JOIN so employees without managers are excluded automatically. This self-join pattern is very common in SQL interviews. Full explanation: youtu.be/u2qBnQya_2E?si… #SQL #DataAnalytics #SQLInterviewQuestions #TheCodingCo

So we need two roles: Employee Manager From the same table. Solution: Self join Employees table e.manager_id = m.employee_id Then compare: e.salary > m.salary This gives employees earning more than their manager.

SQL Interview Question #10 🧵 Find employees who earn more than their manager. Sounds simple… but many candidates freeze. The tricky part is not the comparison. It’s understanding the relationship. Employees and managers are stored in the SAME table. manager_id → employee_id

Important: RANK() → multiple rows if tie ROW_NUMBER() → single row This “aggregate + rank” pattern appears in many SQL interviews. Full explanation: youtu.be/THASWgqU8d0?si… #SQL #DataAnalytics #TheCodingCo #SQLInterviewQuestions

Then filter: rnk = 1 This gives the top product for each month.

SQL Interview Question #9 🧵 Find the top-selling product each month. Sounds like GROUP BY… but it’s more than that. Many candidates calculate total sales correctly… but get stuck finding the top product per month.

If the question says “per city”: Add PARTITION BY city This pattern is very common in time-based SQL problems. Full explanation: youtu.be/OKLqNgTe9z8?si… #SQL #DataAnalytics #TheCodingCo #SQLInterviewQuestions

Example: LAG(temperature) OVER (ORDER BY record_date) Then filter: temperature > previous_temperature That’s it.

SQL Interview Question #8 🧵 Find days where temperature was higher than the previous day. Sounds simple… but many candidates struggle. The tricky part is not the comparison. It’s accessing the previous row correctly.

If calculation is per customer: Add PARTITION BY customer_id This pattern is very common in time-based SQL problems. Full explanation: youtu.be/71aUZiMRnKs?si… #SQL #DataAnalytics #TheCodingCo #SQLInterviewQuestions

The real idea: Access the previous row directly. Use LAG() LAG lets you look at a value from the previous row without writing a join. Example: amount + LAG(amount) OVER (ORDER BY transaction_date) First row returns NULL (no previous row). If needed, use ISNULL or COALESCE.

SQL Interview Question #7 🧵 Show current amount + previous amount in the same row. Sounds simple… but many people overcomplicate it. Most candidates think about self joins. But self joins can get messy quickly.

Another clean solution is using NOT EXISTS. Both approaches return customers who never placed an order. Full explanation: youtu.be/6x68LJa8X1s?si… #SQL #DataAnalytics #TheCodingCo #SQLInterviewQuestions

Correct idea: Start with all customers. Then check who failed to match with Orders. Example pattern: LEFT JOIN Orders WHERE o.customer_id IS NULL

SQL Interview Question #6 🧵 Find customers who never placed an order. Sounds simple… but many candidates still get it wrong. Most people immediately write: INNER JOIN Customers and Orders.

LAG and LEAD Used to compare rows with other rows nearby. LAG → previous row LEAD → next row These five functions appear in many SQL interview questions. Full explanation here: youtube.com/watch?v=dO9YnY… #SQL #DataAnalytics #TheCodingCo #SQLInterviewQuestions

RANK Allows ties. But after a tie, rank numbers skip. Example: 1, 2, 2, 4 DENSE_RANK Also allows ties. But does NOT skip numbers. Example: 1, 2, 2, 3

SQL Window Functions every Data Analyst should know 🧵 ROW_NUMBER RANK DENSE_RANK LAG LEAD These functions show up in many SQL interviews. Example question: “Find the second highest salary in each department.”