✅ Data Warehousing Basics 🏢📦

👉 A Data Warehouse is a central repository used to store large volumes of historical data from multiple sources for reporting and analysis.

It is designed for:
• ✔ Business Intelligence BI
• ✔ Reporting
• ✔ Data Analytics
• ✔ Decision-making

🔹 1. What is a Data Warehouse?
A Data Warehouse collects data from different systems into one centralized location.

Example
A retail company stores data from:
• ✔ Sales system
• ✔ Inventory system
• ✔ Customer database
• ✔ Finance system

All this data is combined into a Data Warehouse for analysis.

🔥 2. Why Do We Need a Data Warehouse?
• ✔ Centralized data storage
• ✔ Faster reporting
• ✔ Historical data analysis
• ✔ Better business decisions

🔹 3. Data Warehouse Architecture ⭐
Data Sources
↓
ETL Extract, Transform, Load
↓
Data Warehouse
↓
Reports & Dashboards

🔹 4. What is ETL?
ETL stands for:

✅ Extract
Collect data from different sources.

✅ Transform
Clean, format, and prepare the data.

✅ Load
Store the transformed data in the Data Warehouse.

🔹 5. OLTP vs OLAP ⭐
OLTP | OLAP
---|---
Daily transactions | Data analysis
Fast inserts & updates | Fast reporting
Current data | Historical data

Examples:
• OLTP: Banking transactions, online shopping orders
• OLAP: Sales reports, yearly revenue analysis

🔹 6. Star Schema ⭐
The most common Data Warehouse schema.
It contains:

⭐ Fact Table
Stores measurable values
Example: Sales Amount, Quantity

⭐ Dimension Tables
Store descriptive information
Example: Customer, Product, Date

🔹 7. Snowflake Schema
Similar to Star Schema but with normalized dimension tables.
👉 Uses more tables and relationships.

🔹 8. Popular Data Warehousing Tools
• ✔ Snowflake
• ✔ Google BigQuery
• ✔ Amazon Redshift
• ✔ Azure Synapse Analytics

🔹 9. Why Data Warehousing is Important?
• ✔ Stores large amounts of data
• ✔ Supports business intelligence
• ✔ Enables faster analytics
• ✔ Frequently asked in interviews

🎯 Today's Goal
• ✔ Understand Data Warehouse concepts
• ✔ Learn ETL process
• ✔ Differentiate OLTP vs OLAP
• ✔ Understand Star Schema & Fact/Dimension tables

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