Database.Middle.What is a star schema? How is it different from a snowflake schema?

A star schema and a snowflake schema are two common ways to design a data warehouse for analytical queries. They define how fact and dimension tables are organized and related.

⭐ Star Schema

Structure:

• A central fact table with foreign keys to several denormalized dimension tables.
• Looks like a star: the fact table is at the center, and dimension tables radiate out.

           Time
             |
Product — Fact — Customer
             |
          Location

✅ Characteristics:

• Dimension tables are flat (denormalized): all attributes in one table.
• Simple structure, easy to query with JOINs.
• Preferred for read-heavy analytical workloads.

✅ Pros:

• Fast query performance (fewer joins)
• Easy to understand and write SQL for
• Optimized for OLAP tools (like Power BI, Tableau)

❌ Cons:

• Data redundancy in dimensions
• Less normalized = more storage

❄️ Snowflake Schema

Structure:

• Similar to star schema, but dimension tables are normalized into sub-dimensions.
• The “arms” of the star have branches — looks like a snowflake.

✅ Characteristics:

• Dimension tables are normalized: broken into multiple related tables.
• More complex joins required.

✅ Pros:

• Saves storage space (removes redundancy)
• Better data integrity (fewer repeated values)

❌ Cons:

• Slower queries due to more joins
• More complex SQL
• Harder for BI tools and analysts

🧠 Key Differences

Feature	Star Schema	Snowflake Schema
Dimension Tables	Denormalized (flat)	Normalized (with sub-dimensions)
Query Speed	Faster	Slower (more joins)
Storage	Uses more space	More space-efficient
Simplicity	Easier to understand and query	More complex
Maintenance	Easier	More effort (more tables/relationships)
Use Case	OLAP reporting, dashboards	Data models with strict normalization

✅ When to Use

Use Case	Recommended Schema
Fast analytics, BI tools	Star Schema
Complex relationships, limited storage	Snowflake Schema
Data marts, simple dashboards	Star Schema
Data lakes with many dependencies	Snowflake Schema