Star Schema vs. Snowflake Schema

Star Schema and Snowflake Schema are two types of dimensional data models used in data warehousing. They help organize data for efficient querying and reporting, especially in OLAP (Online Analytical Processing) systems like Tableau, Power BI, and other BI tools.

1. Star Schema

Definition

A Star Schema is a simpler and denormalized structure where a central fact table is connected to dimension tables, forming a star-like shape.

Structure

• Fact Table: Stores quantitative data (measurable facts) like sales, revenue, etc.

• Dimension Tables: Contain descriptive data (attributes) such as date, customer, product, etc.

Example (Retail Sales Data)

Fact Table (Sales_Fact):

• Sales_ID (PK), Product_ID (FK), Customer_ID (FK), Store_ID (FK), Sales_Amount, Quantity_Sold

Dimension Tables:

• Product_Dim (Product_ID, Product_Name, Category, Price)

• Customer_Dim (Customer_ID, Name, Age, Location)

• Store_Dim (Store_ID, Store_Name, Region)

• Date_Dim (Date_ID, Year, Month, Day, Quarter)

Advantages:

• Simple structure, easy to understand and query

• Faster performance due to fewer joins

• Ideal for BI and reporting tools

Disadvantages:

• Data redundancy (repeated values in dimension tables)

• Larger storage space required

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2. Snowflake Schema

Definition

A Snowflake Schema is a normalized version of the Star Schema where dimension tables are further split into multiple related tables, reducing redundancy.

Structure

• Fact Table: Same as Star Schema

• Dimension Tables: Further normalized into sub-dimensions

Example (Retail Sales Data)

Fact Table (Sales_Fact): (Same as Star Schema)

Dimension Tables:

• Product_Dim (Product_ID, Category_ID, Price)

• Category_Dim (Category_ID, Category_Name)

• Customer_Dim (Customer_ID, Name, Location_ID)

• Location_Dim (Location_ID, Country, State, City)

• Store_Dim (Store_ID, Region_ID)

• Region_Dim (Region_ID, Region_Name)

• Date_Dim (Date_ID, Year, Month, Quarter, Day)

Advantages:

• Reduces data redundancy and saves storage

• Better data integrity and consistency

• More efficient updates

Disadvantages:

• More complex queries due to multiple joins

• Slower performance compared to Star Schema

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Star Schema vs. Snowflake Schema Comparison

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Which One Should You Use?

• Use Star Schema if you prioritize query performance and simplicity (e.g., Tableau dashboards, quick reports).

• Use Snowflake Schema if you need data integrity, storage efficiency, and better data consistency in large databases.