SQL Interview Questions !!

🎗 Write a query to find all employees whose salaries exceed the company's average salary.
🎗 Write a query to retrieve the names of employees who work in the same department as 'John Doe'.
🎗 Write a query to display the second highest salary from the Employee table without using the MAX function twice.
🎗 Write a query to find all customers who have placed more than five orders.
🎗 Write a query to count the total number of orders placed by each customer.
🎗 Write a query to list employees who joined the company within the last 6 months.
🎗 Write a query to calculate the total sales amount for each product.
🎗 Write a query to list all products that have never been sold.
🎗 Write a query to remove duplicate rows from a table.
🎗 Write a query to identify the top 10 customers who have not placed any orders in the past year.

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📊 Data Analyst Roadmap (2025)

Master the Skills That Top Companies Are Hiring For!

📍 1. Learn Excel / Google Sheets
Basic formulas & formatting
VLOOKUP, Pivot Tables, Charts
Data cleaning & conditional formatting

📍 2. Master SQL
SELECT, WHERE, ORDER BY
JOINs (INNER, LEFT, RIGHT)
GROUP BY, HAVING, LIMIT
Subqueries, CTEs, Window Functions

📍 3. Learn Data Visualization Tools
Power BI / Tableau (choose one)
Charts, filters, slicers
Dashboards & storytelling

📍 4. Get Comfortable with Statistics
Mean, Median, Mode, Std Dev
Probability basics
A/B Testing, Hypothesis Testing
Correlation & Regression

📍 5. Learn Python for Data Analysis (Optional but Powerful)
Pandas & NumPy for data handling
Seaborn, Matplotlib for visuals
Jupyter Notebooks for analysis

📍 6. Data Cleaning & Wrangling
Handle missing values
Fix data types, remove duplicates
Text processing & date formatting

📍 7. Understand Business Metrics
KPIs: Revenue, Churn, CAC, LTV
Think like a business analyst
Deliver actionable insights

📍 8. Communication & Storytelling
Present insights with clarity
Simplify complex data
Speak the language of stakeholders

📍 9. Version Control (Git & GitHub)
Track your projects
Build a data portfolio
Collaborate with the community

📍 10. Interview & Resume Preparation
Excel, SQL, case-based questions
Mock interviews + real projects
Resume with measurable achievements

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Step-by-Step Approach to Learn Data Analytics

➊ Learn Programming Language → SQL & Python
↓
➋ Master Excel & Spreadsheets → Pivot Tables, VLOOKUP, Data Cleaning
↓
➌ SQL for Data Analysis → SELECT, JOINS, GROUP BY, Window Functions
↓
➍ Data Manipulation & Processing → Pandas, NumPy
↓
➎ Data Visualization → Power BI, Tableau, Matplotlib, Seaborn
↓
➏ Exploratory Data Analysis (EDA) → Missing Values, Outliers, Feature Engineering
↓
➐ Business Intelligence & Reporting → Dashboards, Storytelling with Data
↓
➑ Advanced Concepts → A/B Testing, Statistical Analysis, Machine Learning Basics

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📊 Data Analyst Roadmap (2025)

Master the Skills That Top Companies Are Hiring For!

📍 1. Learn Excel / Google Sheets
Basic formulas & formatting
VLOOKUP, Pivot Tables, Charts
Data cleaning & conditional formatting

📍 2. Master SQL
SELECT, WHERE, ORDER BY
JOINs (INNER, LEFT, RIGHT)
GROUP BY, HAVING, LIMIT
Subqueries, CTEs, Window Functions

📍 3. Learn Data Visualization Tools
Power BI / Tableau (choose one)
Charts, filters, slicers
Dashboards & storytelling

📍 4. Get Comfortable with Statistics
Mean, Median, Mode, Std Dev
Probability basics
A/B Testing, Hypothesis Testing
Correlation & Regression

📍 5. Learn Python for Data Analysis (Optional but Powerful)
Pandas & NumPy for data handling
Seaborn, Matplotlib for visuals
Jupyter Notebooks for analysis

📍 6. Data Cleaning & Wrangling
Handle missing values
Fix data types, remove duplicates
Text processing & date formatting

📍 7. Understand Business Metrics
KPIs: Revenue, Churn, CAC, LTV
Think like a business analyst
Deliver actionable insights

📍 8. Communication & Storytelling
Present insights with clarity
Simplify complex data
Speak the language of stakeholders

📍 9. Version Control (Git & GitHub)
Track your projects
Build a data portfolio
Collaborate with the community

📍 10. Interview & Resume Preparation
Excel, SQL, case-based questions
Mock interviews + real projects
Resume with measurable achievements

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SQL Advanced Concepts for Data Analyst Interviews

1. Window Functions: Gain proficiency in window functions like ROW_NUMBER(), RANK(), DENSE_RANK(), NTILE(), and LAG()/LEAD(). These functions allow you to perform calculations across a set of table rows related to the current row without collapsing the result set into a single output.

2. Common Table Expressions (CTEs): Understand how to use CTEs with the WITH clause to create temporary result sets that can be referenced within a SELECT, INSERT, UPDATE, or DELETE statement. CTEs improve the readability and maintainability of complex queries.

3. Recursive CTEs: Learn how to use recursive CTEs to solve hierarchical or recursive data problems, such as navigating organizational charts or bill-of-materials structures.

4. Advanced Joins: Master complex join techniques, including self-joins (joining a table with itself), cross joins (Cartesian product), and using multiple joins in a single query.

5. Subqueries and Correlated Subqueries: Be adept at writing subqueries that return a single value or a set of values. Correlated subqueries, which reference columns from the outer query, are particularly powerful for row-by-row operations.

6. Indexing Strategies: Learn advanced indexing strategies, such as covering indexes, composite indexes, and partial indexes. Understand how to optimize query performance by designing the right indexes and when to use CLUSTERED versus NON-CLUSTERED indexes.

7. Query Optimization and Execution Plans: Develop skills in reading and interpreting SQL execution plans to understand how queries are executed. Use tools like EXPLAIN or EXPLAIN ANALYZE to identify performance bottlenecks and optimize query performance.

8. Stored Procedures: Understand how to create and use stored procedures to encapsulate complex SQL logic into reusable, modular code. Learn how to pass parameters, handle errors, and return multiple result sets from a stored procedure.

9. Triggers: Learn how to create triggers to automatically execute a specified action in response to certain events on a table (e.g., AFTER INSERT, BEFORE UPDATE). Triggers are useful for maintaining data integrity and automating workflows.

10. Transactions and Isolation Levels: Master the use of transactions to ensure that a series of SQL operations are executed as a single unit of work. Understand different isolation levels (READ UNCOMMITTED, READ COMMITTED, REPEATABLE READ, SERIALIZABLE) and their impact on data consistency and concurrency.

11. PIVOT and UNPIVOT: Use the PIVOT operator to transform row data into columnar data and UNPIVOT to convert columns back into rows. These operations are crucial for reshaping data for reporting and analysis.

12. Dynamic SQL: Learn how to write dynamic SQL queries that are constructed and executed at runtime. This is useful when the exact SQL query cannot be determined until runtime, such as in scenarios involving user-defined filters or conditional logic.

13. Data Partitioning: Understand how to implement data partitioning strategies, such as range partitioning or list partitioning, to manage large tables efficiently. Partitioning can significantly improve query performance and manageability.

14. Temporary Tables: Learn how to create and use temporary tables to store intermediate results within a session. Understand the differences between local and global temporary tables, and when to use them.

15. Materialized Views: Use materialized views to store the result of a query physically and update it periodically. This can drastically improve performance for complex queries that need to be executed frequently.

16. Handling Complex Data Types: Understand how to work with complex data types such as JSON, XML, and arrays. Learn how to store, query, and manipulate these types in SQL databases, including using functions like JSON_EXTRACT(), XMLQUERY(), or array functions.

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🎯 𝐄𝐬𝐬𝐞𝐧𝐭𝐢𝐚𝐥 𝐃𝐀𝐓𝐀 𝐀𝐍𝐀𝐋𝐘𝐒𝐓 𝐒𝐊𝐈𝐋𝐋𝐒 𝐓𝐡𝐚𝐭 𝐑𝐞𝐜𝐫𝐮𝐢𝐭𝐞𝐫𝐬 𝐋𝐨𝐨𝐤 𝐅𝐨𝐫 🎯

If you're applying for Data Analyst roles, having technical skills like SQL and Power BI is important—but recruiters look for more than just tools!

🔹 1️⃣ 𝐒𝐐𝐋 𝐢𝐬 𝐊𝐈𝐍𝐆 👑—𝐌𝐚𝐬𝐭𝐞𝐫 𝐈𝐭
✅ Know how to write optimized queries (not just SELECT * from everywhere!)
✅ Be comfortable with JOINS, CTEs, Window Functions & Performance Optimization
✅ Practice solving real-world business scenarios using SQL
💡 Example Question: How would you find the top 5 best-selling products in each category using SQL?

🔹 2️⃣ 𝐁𝐮𝐬𝐢𝐧𝐞𝐬𝐬 𝐀𝐜𝐮𝐦𝐞𝐧: 𝐓𝐡𝐢𝐧𝐤 𝐋𝐢𝐤𝐞 𝐚 𝐃𝐞𝐜𝐢𝐬𝐢𝐨𝐧-𝐌𝐚𝐤𝐞𝐫
✅ Understand the why behind the data—not just the numbers
✅ Learn how to frame insights for different stakeholders (Tech & Non-Tech)
✅ Use data storytelling—simplify complex findings into actionable takeaways
💡 Example: Instead of saying, "Revenue increased by 12%," say "Revenue increased 12% after launching a targeted discount campaign, driving a 20% increase in repeat purchases."

🔹 3️⃣ 𝐏𝐨𝐰𝐞𝐫 𝐁𝐈 / 𝐓𝐚𝐛𝐥𝐞𝐚𝐮—𝐌𝐚𝐤𝐞 𝐃𝐚𝐬𝐡𝐛𝐨𝐚𝐫𝐝𝐬 𝐓𝐡𝐚𝐭 𝐒𝐩𝐞𝐚𝐤!
✅ Avoid overloading dashboards with too many visuals—focus on key KPIs
✅ Use interactive elements (filters, drill-throughs) for better usability
✅ Keep visuals simple & clear—bar charts are better than complex pie charts!
💡 Tip: Before creating a dashboard, ask: "What business problem does this solve?"

🔹 4️⃣ 𝐏𝐲𝐭𝐡𝐨𝐧 & 𝐄𝐱𝐜𝐞𝐥—𝐇𝐚𝐧𝐝𝐥𝐞 𝐃𝐚𝐭𝐚 𝐄𝐟𝐟𝐢𝐜𝐢𝐞𝐧𝐭𝐥𝐲
✅ Python for data wrangling, EDA & automation (Pandas, NumPy, Seaborn)
✅ Excel for quick analysis, PivotTables, VLOOKUP/XLOOKUP, Power Query
✅ Know when to use Excel vs. Python (hint: small vs. large datasets)

Being a Data Analyst is more than just running queries—it’s about understanding the business, making insights actionable, and communicating effectively!

Free Resources: https://t.iss.one/sqlspecialist

Tableau Cheat Sheet ✅

This Tableau cheatsheet is designed to be your quick reference guide for data visualization and analysis using Tableau. Whether you’re a beginner learning the basics or an experienced user looking for a handy resource, this cheatsheet covers essential topics.

1. Connecting to Data
- Use *Connect* pane to connect to various data sources (Excel, SQL Server, Text files, etc.).

2. Data Preparation
- Data Interpreter: Clean data automatically using the Data Interpreter.
- Join Data: Combine data from multiple tables using joins (Inner, Left, Right, Outer).
- Union Data: Stack data from multiple tables with the same structure.

3. Creating Views
- Drag & Drop: Drag fields from the Data pane onto Rows, Columns, or Marks to create visualizations.
- Show Me: Use the *Show Me* panel to select different visualization types.

4. Types of Visualizations
- Bar Chart: Compare values across categories.
- Line Chart: Display trends over time.
- Pie Chart: Show proportions of a whole (use sparingly).
- Map: Visualize geographic data.
- Scatter Plot: Show relationships between two variables.

5. Filters
- Dimension Filters: Filter data based on categorical values.
- Measure Filters: Filter data based on numerical values.
- Context Filters: Set a context for other filters to improve performance.

6. Calculated Fields
- Create calculated fields to derive new data:
- Example: Sales Growth = SUM([Sales]) - SUM([Previous Sales])

7. Parameters
- Use parameters to allow user input and control measures dynamically.

8. Formatting
- Format fonts, colors, borders, and lines using the Format pane for better visual appeal.

9. Dashboards
- Combine multiple sheets into a dashboard using the *Dashboard* tab.
- Use dashboard actions (filter, highlight, URL) to create interactivity.

10. Story Points
- Create a story to guide users through insights with narrative and visualizations.

11. Publishing & Sharing
- Publish dashboards to Tableau Server or Tableau Online for sharing and collaboration.

12. Export Options
- Export to PDF or image for offline use.

13. Keyboard Shortcuts
- Show/Hide Sidebar: Ctrl+Alt+T
- Duplicate Sheet: Ctrl + D
- Undo: Ctrl + Z
- Redo: Ctrl + Y

14. Performance Optimization
- Use extracts instead of live connections for faster performance.
- Optimize calculations and filters to improve dashboard loading times.

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Power BI DAX complete Cheatsheet 🧠

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🔟 Data Analyst Project Ideas for Beginners

1. Sales Analysis Dashboard: Use tools like Excel or Tableau to create a dashboard analyzing sales data. Visualize trends, top products, and seasonal patterns.

2. Customer Segmentation: Analyze customer data using clustering techniques (like K-means) to segment customers based on purchasing behavior and demographics.

3. Social Media Metrics Analysis: Gather data from social media platforms to analyze engagement metrics. Create visualizations to highlight trends and performance.

4. Survey Data Analysis: Conduct a survey and analyze the results using statistical techniques. Present findings with visualizations to showcase insights.

5. Exploratory Data Analysis (EDA): Choose a public dataset and perform EDA using Python (Pandas, Matplotlib) or R (tidyverse). Summarize key insights and visualizations.

6. Employee Performance Analysis: Analyze employee performance data to identify trends in productivity, turnover rates, and training effectiveness.

7. Public Health Data Analysis: Use datasets from public health sources (like CDC) to analyze trends in health metrics (e.g., vaccination rates, disease outbreaks) and visualize findings.

8. Real Estate Market Analysis: Analyze real estate listings to find trends in pricing, location, and features. Use data visualization to present your findings.

9. Weather Data Visualization: Collect weather data and analyze trends over time. Create visualizations to show changes in temperature, precipitation, or extreme weather events.

10. Financial Analysis: Analyze a company’s financial statements to assess its performance over time. Create visualizations to highlight key financial ratios and trends.

Data Analytics Resources 👇👇
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Avoid directly copying YouTube projects onto your resume because if everyone looks the same, recruiters might discard resumes.

Instead, for eg, let's say you are working on a SQL case study, download a dataset from Kaggle (usually a CSV file), set up a Postgre/MySQL database, connect it with the data, and prompt ChatGPT with questions ranging from basic to advanced SQL.

Solve the questions step by step. When using PowerBI, connect to the database and create a compelling dashboard. Don't just upload the dataset; employ DAX queries, statistical functions, and avoid relying solely on drag-and-drop features. Use Formatting section to do creative stuff and add your unique element in the project.

ENJOY LEARNING 👍👍

📘 SQL Challenges for Data Analytics – With Explanation 🧠

(Beginner ➡️ Advanced)

1️⃣ Select Specific Columns

SELECT name, email FROM users;

This fetches only the name and email columns from the users table.

✔️ Used when you don’t want all columns from a table.


2️⃣ Filter Records with WHERE

SELECT * FROM users WHERE age > 30;

The WHERE clause filters rows where age is greater than 30.

✔️ Used for applying conditions on data.


3️⃣ ORDER BY Clause

SELECT * FROM users ORDER BY registered_at DESC;

Sorts all users based on registered_at in descending order.
✔️ Helpful to get latest data first.


4️⃣ Aggregate Functions (COUNT, AVG)

SELECT COUNT(*) AS total_users, AVG(age) AS avg_age FROM users;

Explanation:
- COUNT(*) counts total rows (users).
- AVG(age) calculates the average age.
✔️ Used for quick stats from tables.


5️⃣ GROUP BY Usage

SELECT city, COUNT(*) AS user_count FROM users GROUP BY city;

Groups data by city and counts users in each group.

✔️ Use when you want grouped summaries.


6️⃣ JOIN Tables

SELECT users.name, orders.amount  
FROM users  
JOIN orders ON users.id = orders.user_id;

Fetches user names along with order amounts by joining users and orders on matching IDs.
✔️ Essential when combining data from multiple tables.


7️⃣ Use of HAVING

SELECT city, COUNT(*) AS total  
FROM users  
GROUP BY city  
HAVING COUNT(*) > 5;

Like WHERE, but used with aggregates. This filters cities with more than 5 users.
✔️ **Use HAVING after GROUP BY.**


8️⃣ Subqueries

SELECT * FROM users  
WHERE salary > (SELECT AVG(salary) FROM users);

Finds users whose salary is above the average. The subquery calculates the average salary first.

✔️ Nested queries for dynamic filtering9️⃣ CASE Statementnt**

SELECT name,  
  CASE  
    WHEN age < 18 THEN 'Teen'  
    WHEN age <= 40 THEN 'Adult'  
    ELSE 'Senior'  
  END AS age_group  
FROM users;

Adds a new column that classifies users into categories based on age.
✔️ Powerful for conditional logic.

🔟 Window Functions (Advanced)

SELECT name, city, score,  
  RANK() OVER (PARTITION BY city ORDER BY score DESC) AS rank  
FROM users;

Ranks users by score *within each city*.

SQL Learning Series: https://whatsapp.com/channel/0029VanC5rODzgT6TiTGoa1v/1075

Data analytics offers excellent job prospects in 2025, with numerous opportunities across various industries.

Job Market Overview
Data analyst jobs are experiencing rapid growth, with an expected expansion in multiple sectors.

- High Demand Roles:
- Data Scientist
- Business Intelligence Analyst
- Financial Analyst
- Marketing Analyst
- Healthcare Data Analyst

Skills Required
Top skills for success in data analytics include:

- Technical Skills:
- Python and R programming
- SQL database management
- Data manipulation and cleaning
- Statistical analysis
- Power BI or Tableau
- Machine learning basics

Salary Expectations
Average salaries vary by role:
- Data Scientist: ~$122,738 per year
- Data Analyst: Around INR 6L per annum
- Entry-level Data Analyst: ~$83,011 annually[2]

Job Search Strategies

- Utilize job portals like LinkedIn, Indeed & telegram
- Attend industry conferences and webinars
- Network with professionals
- Check company career pages
- Consider recruitment agencies specializing in tech roles

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Data Analyst vs Data Scientist: Must-Know Differences

Data Analyst:
- Role: Primarily focuses on interpreting data, identifying trends, and creating reports that inform business decisions.
- Best For: Individuals who enjoy working with existing data to uncover insights and support decision-making in business processes.
- Key Responsibilities:
- Collecting, cleaning, and organizing data from various sources.
- Performing descriptive analytics to summarize the data (trends, patterns, anomalies).
- Creating reports and dashboards using tools like Excel, SQL, Power BI, and Tableau.
- Collaborating with business stakeholders to provide data-driven insights and recommendations.
- Skills Required:
- Proficiency in data visualization tools (e.g., Power BI, Tableau).
- Strong analytical and statistical skills, along with expertise in SQL and Excel.
- Familiarity with business intelligence and basic programming (optional).
- Outcome: Data analysts provide actionable insights to help companies make informed decisions by analyzing and visualizing data, often focusing on current and historical trends.

Data Scientist:
- Role: Combines statistical methods, machine learning, and programming to build predictive models and derive deeper insights from data.
- Best For: Individuals who enjoy working with complex datasets, developing algorithms, and using advanced analytics to solve business problems.
- Key Responsibilities:
- Designing and developing machine learning models for predictive analytics.
- Collecting, processing, and analyzing large datasets (structured and unstructured).
- Using statistical methods, algorithms, and data mining to uncover hidden patterns.
- Writing and maintaining code in programming languages like Python, R, and SQL.
- Working with big data technologies and cloud platforms for scalable solutions.
- Skills Required:
- Proficiency in programming languages like Python, R, and SQL.
- Strong understanding of machine learning algorithms, statistics, and data modeling.
- Experience with big data tools (e.g., Hadoop, Spark) and cloud platforms (AWS, Azure).
- Outcome: Data scientists develop models that predict future outcomes and drive innovation through advanced analytics, going beyond what has happened to explain why it happened and what will happen next.

Data analysts focus on analyzing and visualizing existing data to provide insights for current business challenges, while data scientists apply advanced algorithms and machine learning to predict future outcomes and derive deeper insights. Data scientists typically handle more complex problems and require a stronger background in statistics, programming, and machine learning.

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Data Science WhatsApp channel: https://whatsapp.com/channel/0029Va8v3eo1NCrQfGMseL2D

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