Why is star schema denormalized?

That is, the dimension tables do not reference any other tables, nor do they have any “sub-dimension tables.” They are generally denormalized because some information may be duplicated in the dimension tables. This allows star schema databases to be optimized for read and query performance along specific dimensions.

Why is Star Schema not normalized?

Star schema dimension tables are not normalized, snowflake schemas dimension tables are normalized. Snowflake schemas will use less space to store dimension tables but are more complex. Star schemas will only join the fact table with the dimension tables, leading to simpler, faster SQL queries.

What is a denormalized schema?

Denormalization is the process of adding precomputed redundant data to an otherwise normalized relational database to improve read performance of the database. Normalizing a database involves removing redundancy so only a single copy exists of each piece of information.

Why is fact table denormalized?

Some say that fact table is in denormalized structure as it might contain the duplicate foreign keys. Fact table ideally contains the aggregatable numeric values and reference keys to the dimension tables for slicing purposes. In some architectures, fact tables could just look like a few columns with numbers.

What are the keys of star schema?

A star schema has one “central” table whose primary key is compound, i.e., consisting of multiple attributes. Each one of these attributes is a foreign key to one of the remaining tables. Such a foreign key dependency exists for each one of these tables, while there are no other foreign keys anywhere in the schema.

What is normalized and denormalized data?

Normalization is the method used in a database to reduce the data redundancy and data inconsistency from the table. By using normalization the number of tables is increased instead of decreased. Denormalization: Denormalization is also the method which is used in a database.

How fact tables are normalized or denormalized?

According to Kimball: Dimensional models combine normalized and denormalized table structures. The dimension tables of descriptive information are highly denormalized with detailed and hierarchical roll-up attributes in the same table. Meanwhile, the fact tables with performance metrics are typically normalized.

What type of relationship does a star schema have between a dimension and fact table?

In a star schema, only single join creates the relationship between the fact table and any dimension tables. A snowflake schema requires many joins to fetch the data.

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