✅SQL Interview Questions with Answers

1️⃣ Write a query to find the second highest salary in the employee table.

SELECT MAX(salary) 
FROM employee 
WHERE salary < (SELECT MAX(salary) FROM employee);

2️⃣ Get the top 3 products by revenue from sales table.

SELECT product_id, SUM(revenue) AS total_revenue 
FROM sales 
GROUP BY product_id 
ORDER BY total_revenue DESC 
LIMIT 3;

3️⃣ Use JOIN to combine customer and order data.

SELECT c.customer_name, o.order_id, o.order_date 
FROM customers c 
JOIN orders o ON c.customer_id = o.customer_id;

(That's an INNER JOIN—use LEFT JOIN to include all customers, even without orders.)

4️⃣ Difference between WHERE and HAVING?
⦁ WHERE filters rows before aggregation (e.g., on individual records).
⦁ HAVING filters rows after aggregation (used with GROUP BY on aggregates). 
  Example:

SELECT department, COUNT(*) 
FROM employee 
GROUP BY department 
HAVING COUNT(*) > 5;

5️⃣ Explain INDEX and how it improves performance. 
An INDEX is a data structure that improves the speed of data retrieval. 
It works like a lookup table and reduces the need to scan every row in a table. 
Especially useful for large datasets and on columns used in WHERE, JOIN, or ORDER BY—think 10x faster queries, but it slows inserts/updates a bit.

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📊 Data Science Essentials: What Every Data Enthusiast Should Know!

1️⃣ Understand Your Data
Always start with data exploration. Check for missing values, outliers, and overall distribution to avoid misleading insights.

2️⃣ Data Cleaning Matters
Noisy data leads to inaccurate predictions. Standardize formats, remove duplicates, and handle missing data effectively.

3️⃣ Use Descriptive & Inferential Statistics
Mean, median, mode, variance, standard deviation, correlation, hypothesis testing—these form the backbone of data interpretation.

4️⃣ Master Data Visualization
Bar charts, histograms, scatter plots, and heatmaps make insights more accessible and actionable.

5️⃣ Learn SQL for Efficient Data Extraction
Write optimized queries (SELECT, JOIN, GROUP BY, WHERE) to retrieve relevant data from databases.

6️⃣ Build Strong Programming Skills
Python (Pandas, NumPy, Scikit-learn) and R are essential for data manipulation and analysis.

7️⃣ Understand Machine Learning Basics
Know key algorithms—linear regression, decision trees, random forests, and clustering—to develop predictive models.

8️⃣ Learn Dashboarding & Storytelling
Power BI and Tableau help convert raw data into actionable insights for stakeholders.

🔥 Pro Tip: Always cross-check your results with different techniques to ensure accuracy!

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Essential Python Libraries to build your career in Data Science 📊👇

1. NumPy:
- Efficient numerical operations and array manipulation.

2. Pandas:
- Data manipulation and analysis with powerful data structures (DataFrame, Series).

3. Matplotlib:
- 2D plotting library for creating visualizations.

4. Seaborn:
- Statistical data visualization built on top of Matplotlib.

5. Scikit-learn:
- Machine learning toolkit for classification, regression, clustering, etc.

6. TensorFlow:
- Open-source machine learning framework for building and deploying ML models.

7. PyTorch:
- Deep learning library, particularly popular for neural network research.

8. SciPy:
- Library for scientific and technical computing.

9. Statsmodels:
- Statistical modeling and econometrics in Python.

10. NLTK (Natural Language Toolkit):
- Tools for working with human language data (text).

11. Gensim:
- Topic modeling and document similarity analysis.

12. Keras:
- High-level neural networks API, running on top of TensorFlow.

13. Plotly:
- Interactive graphing library for making interactive plots.

14. Beautiful Soup:
- Web scraping library for pulling data out of HTML and XML files.

15. OpenCV:
- Library for computer vision tasks.

As a beginner, you can start with Pandas and NumPy for data manipulation and analysis. For data visualization, Matplotlib and Seaborn are great starting points. As you progress, you can explore machine learning with Scikit-learn, TensorFlow, and PyTorch.

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Best Resources to learn Python & Data Science 👇👇

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Best Data Science & Machine Learning Resources

Interview Process for Data Science Role at Amazon

Python Interview Resources

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SQL 𝗢𝗿𝗱𝗲𝗿 𝗢𝗳 𝗘𝘅𝗲𝗰𝘂𝘁𝗶𝗼𝗻 ↓

1 → FROM (Tables selected).
2 → WHERE (Filters applied).
3 → GROUP BY (Rows grouped).
4 → HAVING (Filter on grouped data).
5 → SELECT (Columns selected).
6 → ORDER BY (Sort the data).
7 → LIMIT (Restrict number of rows).

𝗖𝗼𝗺𝗺𝗼𝗻 𝗤𝘂𝗲𝗿𝗶𝗲𝘀 𝗧𝗼 𝗣𝗿𝗮𝗰𝘁𝗶𝗰𝗲 ↓

↬ Find the second-highest salary:

SELECT MAX(Salary) FROM Employees WHERE Salary < (SELECT MAX(Salary) FROM Employees);

↬ Find duplicate records:

SELECT Name, COUNT(*)
FROM Emp
GROUP BY Name
HAVING COUNT(*) > 1;

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4 Career Paths In Data Analytics

1) Data Analyst:

Role: Data Analysts interpret data and provide actionable insights through reports and visualizations.

They focus on querying databases, analyzing trends, and creating dashboards to help businesses make data-driven decisions.

Skills: Proficiency in SQL, Excel, data visualization tools (like Tableau or Power BI), and a good grasp of statistics.

Typical Tasks: Generating reports, creating visualizations, identifying trends and patterns, and presenting findings to stakeholders.


2)Data Scientist:

Role: Data Scientists use advanced statistical techniques, machine learning algorithms, and programming to analyze and interpret complex data.

They develop models to predict future trends and solve intricate problems.
Skills: Strong programming skills (Python, R), knowledge of machine learning, statistical analysis, data manipulation, and data visualization.

Typical Tasks: Building predictive models, performing complex data analyses, developing machine learning algorithms, and working with big data technologies.


3)Business Intelligence (BI) Analyst:

Role: BI Analysts focus on leveraging data to help businesses make strategic decisions.

They create and manage BI tools and systems, analyze business performance, and provide strategic recommendations.

Skills: Experience with BI tools (such as Power BI, Tableau, or Qlik), strong analytical skills, and knowledge of business operations and strategy.

Typical Tasks: Designing and maintaining dashboards and reports, analyzing business performance metrics, and providing insights for strategic planning.

4)Data Engineer:

Role: Data Engineers build and maintain the infrastructure required for data generation, storage, and processing. They ensure that data pipelines are efficient and reliable, and they prepare data for analysis.

Skills: Proficiency in programming languages (such as Python, Java, or Scala), experience with database management systems (SQL and NoSQL), and knowledge of data warehousing and ETL (Extract, Transform, Load) processes.

Typical Tasks: Designing and building data pipelines, managing and optimizing databases, ensuring data quality, and collaborating with data scientists and analysts.

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🚀 Key Skills for Aspiring Tech Specialists

📊 Data Analyst:
- Proficiency in SQL for database querying
- Advanced Excel for data manipulation
- Programming with Python or R for data analysis
- Statistical analysis to understand data trends
- Data visualization tools like Tableau or PowerBI
- Data preprocessing to clean and structure data
- Exploratory data analysis techniques

🧠 Data Scientist:
- Strong knowledge of Python and R for statistical analysis
- Machine learning for predictive modeling
- Deep understanding of mathematics and statistics
- Data wrangling to prepare data for analysis
- Big data platforms like Hadoop or Spark
- Data visualization and communication skills
- Experience with A/B testing frameworks

🏗 Data Engineer:
- Expertise in SQL and NoSQL databases
- Experience with data warehousing solutions
- ETL (Extract, Transform, Load) process knowledge
- Familiarity with big data tools (e.g., Apache Spark)
- Proficient in Python, Java, or Scala
- Knowledge of cloud services like AWS, GCP, or Azure
- Understanding of data pipeline and workflow management tools

🤖 Machine Learning Engineer:
- Proficiency in Python and libraries like scikit-learn, TensorFlow
- Solid understanding of machine learning algorithms
- Experience with neural networks and deep learning frameworks
- Ability to implement models and fine-tune their parameters
- Knowledge of software engineering best practices
- Data modeling and evaluation strategies
- Strong mathematical skills, particularly in linear algebra and calculus

🧠 Deep Learning Engineer:
- Expertise in deep learning frameworks like TensorFlow or PyTorch
- Understanding of Convolutional and Recurrent Neural Networks
- Experience with GPU computing and parallel processing
- Familiarity with computer vision and natural language processing
- Ability to handle large datasets and train complex models
- Research mindset to keep up with the latest developments in deep learning

🤯 AI Engineer:
- Solid foundation in algorithms, logic, and mathematics
- Proficiency in programming languages like Python or C++
- Experience with AI technologies including ML, neural networks, and cognitive computing
- Understanding of AI model deployment and scaling
- Knowledge of AI ethics and responsible AI practices
- Strong problem-solving and analytical skills

🔊 NLP Engineer:
- Background in linguistics and language models
- Proficiency with NLP libraries (e.g., NLTK, spaCy)
- Experience with text preprocessing and tokenization
- Understanding of sentiment analysis, text classification, and named entity recognition
- Familiarity with transformer models like BERT and GPT
- Ability to work with large text datasets and sequential data

🌟 Embrace the world of data and AI, and become the architect of tomorrow's technology!

🚀 Roadmap to Master Data Science in 60 Days! 📊🤖

📅 Week 1–2: Python & Data Handling Basics
- Day 1–5: Python fundamentals — variables, loops, functions, lists, dictionaries
- Day 6–10: NumPy & Pandas — arrays, data cleaning, filtering, data manipulation

📅 Week 3–4: Data Analysis & Visualization
- Day 11–15: Data analysis — EDA (Exploratory Data Analysis), statistics basics, data preprocessing
- Day 16–20: Data visualization — Matplotlib, Seaborn, charts, dashboards, storytelling with data

📅 Week 5–6: Machine Learning Fundamentals
- Day 21–25: ML concepts — supervised vs unsupervised learning, regression, classification
- Day 26–30: ML algorithms — Linear Regression, Logistic Regression, Decision Trees, KNN

📅 Week 7–8: Advanced ML & Model Building
- Day 31–35: Model evaluation — train/test split, cross-validation, accuracy, precision, recall
- Day 36–40: Scikit-learn, feature engineering, model tuning, clustering (K-Means)

📅 Week 9: SQL & Real-World Data Skills
- Day 41–45: SQL — SELECT, WHERE, JOIN, GROUP BY, subqueries
- Day 46–50: Working with real datasets, Kaggle practice, data pipelines basics

📅 Final Days: Projects + Deployment
- Day 51–60:
– Build 2–3 projects (sales prediction, customer segmentation, recommendation system)
– Create portfolio on GitHub
– Learn basics of model deployment (Streamlit/Flask)
– Prepare for data science interviews

⭐ Bonus Tip: Focus more on projects than theory — companies hire for practical skills.

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❌ Power BI alone won’t make you Data Analyst
❌ Power BI cannot get you a 18 LPA job offer
❌ Power BI cannot be mastered in 2 days
❌ Power BI is not just colorful dashboard
❌ Power BI is not simple “drag and drop”
❌ Power BI isn’t for Data Analysts only

But here’s what Power BI can do:

✔️ Power BI can save your reporting time
✔️ Power BI keeps your confidential data safe
✔️ Power BI helps you say bye to Pivot Tables
✔️ Power BI makes your report easy to consume
✔️ Power BI can update your dashboard with a single click
✔️ Power BI handles heavy data without testing your patience
✔️ Power BI is the next level for people whose work depends on Excel


I can go on and on, but you get the point.

Wrong expectations -> Wrong results
Right expectations -> Amazing results