Friday, December 14, 2012

Star Schema and Snowflake Schema

What is Star schema and SnowFlake schema?

Star Schema: A Star schema is a schema in which a fact is connected to multiple dimensions and dimension table doesn't have any parent table.




Snowflake Schema: A SnowFlake schema is a schema in which a fact is connected to multiple dimensions and dimension table have one or more parent table. In other words, snowflake schema is "a star schema with   dimensions connected to some more dimensions"





Star Schema vs Snowflake schema
Star Schema Snowflake Schema

Has data redundancy(duplicate data) and difficult
to maintain
No data redundancy and easy to maintain
Has De-normalized tables
Has Normalized tables
Suitable for large datawarehouse
Suitable for small datawarehouse
Dimension table is not connected to other dimension table
Dimension table is connected to another dimension table
Queries are less complex and easy to understand
Queries are more complex and difficult to understand
Has less number of joins
Has more number of joins
Less query execution time
More execution time because of complex queries

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