ETL vs ELT – Explained Using Apple Juice analogy! 🍎🧃

We often hear about ETL and ELT in the data world — but how do they actually apply in tools like Excel and Power BI?

Let’s break it down with a simple and relatable analogy 👇

✅ ETL (Extract → Transform → Load)

🧃 First you make the juice, then you deliver it

➡️ Apples → Juice → Truck

🔹 In Power BI / Excel:

You clean and transform the data in Power Query
Then load the final data into your report or sheet
💡 That’s ETL – transformation happens before loading



✅ ELT (Extract → Load → Transform)

🍏 First you deliver the apples, and make juice later

➡️ Apples → Truck → Juice

🔹 In Power BI / Excel:

You load raw data into your model or sheet
Then transform it using DAX, formulas, or pivot tables
💡 That’s ELT – transformation happens after loading

Adaptive Query Execution (AQE) in Apache Spark is a feature introduced to improve query performance dynamically at runtime, based on actual data statistics collected during execution.

This makes Spark smarter and more efficient, especially when dealing with real-world messy data where planning ahead (at compile time) might be misleading.

🔍 Importance of AQE in Spark
Runtime Optimization:

AQE adapts the execution plan on the fly using real-time stats, fixing issues that static planning can't predict.

Better Join Strategy:
If Spark detects at runtime that one table is smaller than expected, it can switch to a broadcast join instead of a slower shuffle join.

Improved Resource Usage:
By optimizing stage sizes and join plans, AQE avoids unnecessary shuffling and memory usage, leading to faster execution and lower cost.


🪓 Handling Data Skew with AQE
Data skew occurs when some partitions (e.g., specific keys) have much more data than others, slowing down those tasks.

AQE handles this using:

Skew Join Optimization:
AQE detects skewed partitions and breaks them into smaller sub-partitions, allowing Spark to process them in parallel instead of waiting on one giant slow task.

Automatic Repartitioning:
It can dynamically adjust partition sizes for better load balancing, reducing the "straggler" effect from skew.


💡 Example:
If a join key like customer_id = 12345 appears millions of times more than others, Spark can split just that key’s data into chunks, while keeping others untouched. This makes the whole join process more balanced and efficient.

In summary, AQE improves performance, handles skew gracefully, and makes Spark queries more resilient and adaptive—especially useful in big, uneven datasets.

📘 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 Engineering Roadmap 2025

𝟭. 𝗖𝗹𝗼𝘂𝗱 𝗦𝗤𝗟 (𝗔𝗪𝗦 𝗥𝗗𝗦, 𝗚𝗼𝗼𝗴𝗹𝗲 𝗖𝗹𝗼𝘂𝗱 𝗦𝗤𝗟, 𝗔𝘇𝘂𝗿𝗲 𝗦𝗤𝗟)

💡 Why? Cloud-managed databases are the backbone of modern data platforms.

✅ Serverless, scalable, and cost-efficient
✅ Automated backups & high availability
✅ Works seamlessly with cloud data pipelines

𝟮. 𝗱𝗯𝘁 (𝗗𝗮𝘁𝗮 𝗕𝘂𝗶𝗹𝗱 𝗧𝗼𝗼𝗹) – 𝗧𝗵𝗲 𝗙𝘂𝘁𝘂𝗿𝗲 𝗼𝗳 𝗘𝗟𝗧

💡 Why? Transform data inside your warehouse (Snowflake, BigQuery, Redshift).

✅ SQL-based transformation – easy to learn
✅ Version control & modular data modeling
✅ Automates testing & documentation

𝟯. 𝗔𝗽𝗮𝗰𝗵𝗲 𝗔𝗶𝗿𝗳𝗹𝗼𝘄 – 𝗪𝗼𝗿𝗸𝗳𝗹𝗼𝘄 𝗢𝗿𝗰𝗵𝗲𝘀𝘁𝗿𝗮𝘁𝗶𝗼𝗻

💡 Why? Automate and schedule complex ETL/ELT workflows.

✅ DAG-based orchestration for dependency management
✅ Integrates with cloud services (AWS, GCP, Azure)
✅ Highly scalable & supports parallel execution

𝟰. 𝗗𝗲𝗹𝘁𝗮 𝗟𝗮𝗸𝗲 – 𝗧𝗵𝗲 𝗣𝗼𝘄𝗲𝗿 𝗼𝗳 𝗔𝗖𝗜𝗗 𝗶𝗻 𝗗𝗮𝘁𝗮 𝗟𝗮𝗸𝗲𝘀

💡 Why? Solves data consistency & reliability issues in Apache Spark & Databricks.
✅ Supports ACID transactions in data lakes
✅ Schema evolution & time travel
✅ Enables incremental data processing

𝟱. 𝗖𝗹𝗼𝘂𝗱 𝗗𝗮𝘁𝗮 𝗪𝗮𝗿𝗲𝗵𝗼𝘂𝘀𝗲𝘀 (𝗦𝗻𝗼𝘄𝗳𝗹𝗮𝗸𝗲, 𝗕𝗶𝗴𝗤𝘂𝗲𝗿𝘆, 𝗥𝗲𝗱𝘀𝗵𝗶𝗳𝘁)

💡 Why? Centralized, scalable, and powerful for analytics.
✅ Handles petabytes of data efficiently
✅ Pay-per-use pricing & serverless architecture

𝟲. 𝗔𝗽𝗮𝗰𝗵𝗲 𝗞𝗮𝗳𝗸𝗮 – 𝗥𝗲𝗮𝗹-𝗧𝗶𝗺𝗲 𝗦𝘁𝗿𝗲𝗮𝗺𝗶𝗻𝗴

💡 Why? For real-time event-driven architectures.
✅ High-throughput

𝟳. 𝗣𝘆𝘁𝗵𝗼𝗻 & 𝗦𝗤𝗟 – 𝗧𝗵𝗲 𝗖𝗼𝗿𝗲 𝗼𝗳 𝗗𝗮𝘁𝗮 𝗘𝗻𝗴𝗶𝗻𝗲𝗲𝗿𝗶𝗻𝗴

💡 Why? Every data engineer must master these!

✅ SQL for querying, transformations & performance tuning
✅ Python for automation, data processing, and API integrations

𝟴. 𝗗𝗮𝘁𝗮𝗯𝗿𝗶𝗰𝗸𝘀 – 𝗨𝗻𝗶𝗳𝗶𝗲𝗱 𝗔𝗻𝗮𝗹𝘆𝘁𝗶𝗰𝘀 & 𝗔𝗜

💡 Why? The go-to platform for big data processing & machine learning on the cloud.

✅ Built on Apache Spark for fast distributed computing

Lol 🤣

𝐈𝐟 𝐲𝐨𝐮'𝐫𝐞 𝐚 𝐃𝐚𝐭𝐚 𝐄𝐧𝐠𝐢𝐧𝐞𝐞𝐫 𝐰𝐨𝐫𝐤𝐢𝐧𝐠 𝐰𝐢𝐭𝐡 𝐛𝐢𝐠 𝐝𝐚𝐭𝐚 - 𝐏𝐲𝐒𝐩𝐚𝐫𝐤 𝐢𝐬 𝐲𝐨𝐮𝐫 𝐛𝐞𝐬𝐭 𝐟𝐫𝐢𝐞𝐧𝐝.⁣
⁣
Whether you're building data pipelines, transforming terabytes of logs, or cleaning data for analytics, PySpark helps you scale Python across distributed systems with ease.⁣
⁣
Here are a few PySpark fundamentals every Data Engineer should be confident with:⁣
⁣
𝟏. 𝐑𝐞𝐚𝐝𝐢𝐧𝐠 𝐝𝐚𝐭𝐚 𝐞𝐟𝐟𝐢𝐜𝐢𝐞𝐧𝐭𝐥𝐲⁣
⁣
spark.read.csv(), json(), parquet()⁣
⁣
Choose the right format for performance.⁣
⁣
𝟐. 𝐂𝐨𝐫𝐞 𝐭𝐫𝐚𝐧𝐬𝐟𝐨𝐫𝐦𝐚𝐭𝐢𝐨𝐧𝐬⁣
⁣
map, flatMap, filter, union⁣
⁣
Understand how these shape your RDDs or DataFrames.⁣
⁣
𝟑. 𝐀𝐠𝐠𝐫𝐞𝐠𝐚𝐭𝐢𝐨𝐧𝐬 𝐚𝐭 𝐬𝐜𝐚𝐥𝐞⁣
⁣
groupBy, agg, .count()⁣
⁣
Use them to build clean summaries and insights from raw data.⁣
⁣
𝟒. 𝐂𝐨𝐥𝐮𝐦𝐧 𝐦𝐚𝐧𝐢𝐩𝐮𝐥𝐚𝐭𝐢𝐨𝐧𝐬⁣
⁣
withColumn() is a go-to tool for feature engineering or adding derived columns.⁣
⁣
Data Engineering is about building scalable, reliable, and efficient systems-and PySpark makes that possible when you're working with huge datasets.

React ♥️ for more

Roadmap to Become a Data Engineer in 10 Stages

Stage 1 → SQL & Database Fundamentals
Stage 2 → Python for Data Engineering (Pandas, PySpark)
Stage 3 → Data Modelling & ETL/ELT Design (Star Schema, CDC, DWH)
Stage 4 → Big Data Tools (Apache Spark, Kafka, Hive)
Stage 5 → Cloud Platforms (Azure / AWS / GCP)
Stage 6 → Data Orchestration (Airflow, ADF, Prefect, DBT)
Stage 7 → Data Lakes & Warehouses (Delta Lake, Snowflake, BigQuery)
Stage 8 → Monitoring, Testing & Governance (Great Expectations, DataDog)
Stage 9 → Real-Time Pipelines (Kafka, Flink, Kinesis)
Stage 10 → CI/CD & DevOps for Data (GitHub Actions, Terraform, Docker)

👉 You don’t need to learn everything at once.
👉 Build around one stack, skip a few steps if you’re just starting out.
👉 Master fundamentals first, then move to the cloud.

The key is consistency → take it step by step and grow your skill set!

FREE RESOURCES TO LEARN DATA ENGINEERING
👇👇

Big Data and Hadoop Essentials free course

https://bit.ly/3rLxbul

Data Engineer: Prepare Financial Data for ML and Backtesting FREE UDEMY COURSE
[4.6 stars out of 5]

https://bit.ly/3fGRjLu

Understanding Data Engineering from Datacamp

https://clnk.in/soLY

Data Engineering Free Books

https://ia600201.us.archive.org/4/items/springer_10.1007-978-1-4419-0176-7/10.1007-978-1-4419-0176-7.pdf

https://www.darwinpricing.com/training/Data_Engineering_Cookbook.pdf

Big Data of Data Engineering Free book

https://databricks.com/wp-content/uploads/2021/10/Big-Book-of-Data-Engineering-Final.pdf

https://aimlcommunity.com/wp-content/uploads/2019/09/Data-Engineering.pdf

The Data Engineer’s Guide to Apache Spark

https://news.1rj.ru/str/datasciencefun/783

Data Engineering with Python

https://news.1rj.ru/str/pythondevelopersindia/343

Data Engineering Projects -

1.End-To-End From Web Scraping to Tableau  https://lnkd.in/ePMw63ge

2. Building Data Model and Writing ETL Job https://lnkd.in/eq-e3_3J

3. Data Modeling and Analysis using Semantic Web Technologies https://lnkd.in/e4A86Ypq

4. ETL Project in Azure Data Factory - https://lnkd.in/eP8huQW3

5. ETL Pipeline on AWS Cloud - https://lnkd.in/ebgNtNRR

6. Covid Data Analysis Project - https://lnkd.in/eWZ3JfKD

7. YouTube Data Analysis 
   (End-To-End Data Engineering Project) - https://lnkd.in/eYJTEKwF

8. Twitter Data Pipeline using Airflow - https://lnkd.in/eNxHHZbY

9. Sentiment analysis Twitter:
    Kafka and Spark Structured Streaming -  https://lnkd.in/esVAaqtU

ENJOY LEARNING 👍👍

📌 🚀 How to Build a Personal Brand as a Data Analyst

Want to stand out in the competitive job market? Build your personal brand using these strategies:

✅ 1. Share Your Work Publicly – Post SQL/Python projects on LinkedIn, Medium, or GitHub.

✅ 2. Engage with Data Communities – Follow & contribute to Kaggle, DataCamp, or Analytics Vidhya.

✅ 3. Write About Data – Share blog posts on real-world data insights & case studies.

✅ 4. Present at Meetups/Webinars – Gain visibility & network with industry experts.

✅ 5. Optimize LinkedIn & GitHub – Highlight your skills, certifications, and projects.


💡 Start with one personal branding activity this week.

Q: How do you import data from various sources (Excel, SQL Server, CSV) into Power BI?

A: Here’s how to handle multi-source imports in Power BI Desktop:

1. Excel:

° Go to Home > Get Data > Excel

° Select your file & sheets or tables



2. CSV:

° Choose Get Data > Text/CSV

° Browse and load the file



3. SQL Server:

° Select Get Data > SQL Server

° Enter server/database name

° Use a query or select tables directly



4. Combine Sources:

° Use Power Query to transform, merge, or append tables

° Create relationships in the Model view


Pro Tip:
Use consistent data types and naming to make transformations smoother across sources!

ChatGPT Prompt to learn any skill
👇👇
I am seeking to become an expert professional in [Making ChatGPT prompts perfectly]. I would like ChatGPT to provide me with a complete course on this subject, following the principles of Pareto principle and simulating the complexity, structure, duration, and quality of the information found in a college degree program at a prestigious university. The course should cover the following aspects: Course Duration: The course should be structured as a comprehensive program, spanning a duration equivalent to a full-time college degree program, typically four years. Curriculum Structure: The curriculum should be well-organized and divided into semesters or modules, progressing from beginner to advanced levels of proficiency. Each semester/module should have a logical flow and build upon the previous knowledge. Relevant and Accurate Information: The course should provide all the necessary and up-to-date information required to master the skill or knowledge area. It should cover both theoretical concepts and practical applications. Projects and Assignments: The course should include a series of hands-on projects and assignments that allow me to apply the knowledge gained. These projects should range in complexity, starting from basic exercises and gradually advancing to more challenging real-world applications. Learning Resources: ChatGPT should share a variety of learning resources, including textbooks, research papers, online tutorials, video lectures, practice exams, and any other relevant materials that can enhance the learning experience. Expert Guidance: ChatGPT should provide expert guidance throughout the course, answering questions, providing clarifications, and offering additional insights to deepen understanding. I understand that ChatGPT's responses will be generated based on the information it has been trained on and the knowledge it has up until September 2021. However, I expect the course to be as complete and accurate as possible within these limitations. Please provide the course syllabus, including a breakdown of topics to be covered in each semester/module, recommended learning resources, and any other relevant information

(Tap on above text to copy)

🚀 PyTorch vs TensorFlow – Which Should YOU Choose?

If you’re starting in AI or planning to build real-world apps, this is the big question.

👉 PyTorch – simple, feels like Python, runs instantly. Perfect for learning, experiments, and research.
👉 TensorFlow – built by Google, comes with a full production toolkit (mobile, web, cloud). Perfect for apps at scale.

✨ Developer Experience: PyTorch is beginner-friendly. TensorFlow has improved with Keras but still leans towards production use.
📊 Research vs Production: 75% of research papers use PyTorch, but TensorFlow powers large-scale deployments.

💡 Think of it like this:
PyTorch = Notebook for experiments ✍️
TensorFlow = Office suite for real apps 🏢

So the choice is simple:

Learning & Research → PyTorch

Scaling & Deployment → TensorFlow

Amazon Interview Process for Data Scientist position

📍Round 1- Phone Screen round
This was a preliminary round to check my capability, projects to coding, Stats, ML, etc.

After clearing this round the technical Interview rounds started. There were 5-6 rounds (Multiple rounds in one day).

📍 𝗥𝗼𝘂𝗻𝗱 𝟮- 𝗗𝗮𝘁𝗮 𝗦𝗰𝗶𝗲𝗻𝗰𝗲 𝗕𝗿𝗲𝗮𝗱𝘁𝗵:
In this round the interviewer tested my knowledge on different kinds of topics.

📍𝗥𝗼𝘂𝗻𝗱 𝟯- 𝗗𝗲𝗽𝘁𝗵 𝗥𝗼𝘂𝗻𝗱:
In this round the interviewers grilled deeper into 1-2 topics. I was asked questions around:
Standard ML tech, Linear Equation, Techniques, etc.

📍𝗥𝗼𝘂𝗻𝗱 𝟰- 𝗖𝗼𝗱𝗶𝗻𝗴 𝗥𝗼𝘂𝗻𝗱-
This was a Python coding round, which I cleared successfully.

📍𝗥𝗼𝘂𝗻𝗱 𝟱- This was 𝗛𝗶𝗿𝗶𝗻𝗴 𝗠𝗮𝗻𝗮𝗴𝗲𝗿 where my fitment for the team got assessed.

📍𝗟𝗮𝘀𝘁 𝗥𝗼𝘂𝗻𝗱- 𝗕𝗮𝗿 𝗥𝗮𝗶𝘀𝗲𝗿- Very important round, I was asked heavily around Leadership principles & Employee dignity questions.

So, here are my Tips if you’re targeting any Data Science role:
-> Never make up stuff & don’t lie in your Resume.
-> Projects thoroughly study.
-> Practice SQL, DSA, Coding problem on Leetcode/Hackerank.
-> Download data from Kaggle & build EDA (Data manipulation questions are asked)

Best Data Science & Machine Learning Resources: https://topmate.io/coding/914624

ENJOY LEARNING 👍👍