🎯 📊 DATA ANALYST MOCK INTERVIEW (WITH ANSWERS)

🧠 1️⃣ Tell me about yourself
✅ Sample Answer:
“I have around 3 years of experience working with data. My core skills include SQL, Excel, and Power BI. I regularly work with data cleaning, transformation, and building dashboards to generate business insights. Recently, I’ve also been strengthening my Python skills for data analysis. I enjoy solving business problems using data and presenting insights in a simple and actionable way.”

📊 2️⃣ What is the difference between WHERE and HAVING?
✅ Answer:
WHERE filters rows before aggregation
HAVING filters after aggregation
Example:
SELECT department, COUNT(*)
FROM employees
GROUP BY department
HAVING COUNT(*) > 5;

🔗 3️⃣ Explain different types of JOINs
✅ Answer:
INNER JOIN → only matching records
LEFT JOIN → all left + matching right
RIGHT JOIN → all right + matching left
FULL JOIN → all records from both
👉 In analytics, LEFT JOIN is most used.

🧠 4️⃣ How do you find duplicate records in SQL?
✅ Answer:
SELECT column, COUNT(*)
FROM table
GROUP BY column
HAVING COUNT(*) > 1;

👉 Used for data cleaning.

📈 5️⃣ What are window functions?
✅ Answer:
“Window functions perform calculations across rows without reducing the number of rows. They are used for ranking, running totals, and comparisons.”
Example:
SELECT salary, RANK() OVER(ORDER BY salary DESC)
FROM employees;

📊 6️⃣ How do you handle missing data?
✅ Answer:
Remove rows (if small impact)
Replace with mean/median
Use default values
Use interpolation (advanced)
👉 Depends on business context.

📉 7️⃣ What is the difference between COUNT(_) and COUNT(column)?
✅ Answer:
COUNT(*) → counts all rows
COUNT(column) → ignores NULL values

📊 8️⃣ What is a KPI? Give example
✅ Answer:
“KPI (Key Performance Indicator) is a measurable value used to track performance.”
Examples: Revenue growth, Conversion rate, Customer retention

🧠 9️⃣ How would you find the 2nd highest salary?
✅ Answer:
SELECT MAX(salary)
FROM employees
WHERE salary < ( SELECT MAX(salary) FROM employees );

📊 🔟 Explain your dashboard project
✅ Strong Answer:
“I created a sales dashboard in Power BI where I analyzed revenue trends, top-performing products, and regional performance. I used DAX for calculations and added filters for better interactivity. This helped stakeholders identify key areas for growth.”

🔥 1️⃣1️⃣ What is normalization?
✅ Answer:
“Normalization is the process of organizing data to reduce redundancy and improve data integrity.”

📊 1️⃣2️⃣ Difference between INNER JOIN and LEFT JOIN?
✅ Answer:
INNER JOIN → only matching data
LEFT JOIN → keeps all left table data
👉 LEFT JOIN is preferred in analytics.

🧠 1️⃣3️⃣ What is a CTE?
✅ Answer:
“A CTE (Common Table Expression) is a temporary result set defined using WITH clause to improve readability.”

📈 1️⃣4️⃣ How do you explain insights to non-technical people?
✅ Answer:
“I focus on storytelling. Instead of technical terms, I explain insights in simple business language with visuals and examples.”

📊 1️⃣5️⃣ What tools have you used?
✅ Answer:
SQL, Excel, Power BI, Python (basic/advanced depending on you)

💼 1️⃣6️⃣ Behavioral Question: Tell me about a challenge
✅ Answer:
“While working on a dataset, I found inconsistencies in data. I cleaned and standardized it using SQL and Excel, ensuring accurate analysis. This improved the dashboard reliability.”

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