🔢 16) How do you merge customer and orders dataframes on customer_id?
👉 Answer:
# Keep all customers (even no orders)
merged = pd.merge(customers, orders, on='customer_id', how='left')
LEFT JOIN = Industry standard for customer analytics!

📉 17) What are 5 must-have KPIs for an e-commerce dashboard?
👉 Answer:
1. Revenue (vs target)
2. AOV
3. Conversion Rate
4. Cart Abandonment
5. Customer Acquisition Cost. Trend + Target + YoY always!

⚙️ 18) Your SQL query is running slow. How do you optimize?
👉 Answer:
Top 5 fixes:
1. Indexes on WHERE/JOIN columns
2. EXPLAIN query plan
3. Avoid SELECT *
4. Limit subqueries
5. Aggregate at source.

🧠 19) Tell me about a time your data analysis failed. What happened?
👉 Answer: Situation: Dashboard showed wrong trends. Problem: Timezone mismatch in sales data. Fix: Added CONVERT_TZ() in SQL + data validation layer. Result: 100% accuracy, saved stakeholder trust.

💬 20) Do you have any questions for us?
👉 Answer: 1. What are the top 3 metrics leadership cares about? 2. What's your biggest data challenge? 3. How do you measure success in this role after 90 days?

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