The star schema (sometimes referenced as star join schema) is the simplest data warehouse schema, consisting of a single "fact table" with a compound primary key, with one segment for each "dimension" and with additional columns of additive, numeric facts. The name star schema is derived from the fact that the schema diagram is shaped like a star. This article or section does not cite its references or sources. ... A fact table is a data warehousing concept. ... In database design, a primary key is a value that can be used to identify a unique row in a table. ... In a data warehouse, a dimension is a data element that categorizes each item in a data set into non-overlapping regions. ...

The star schema makes multi-dimensional database (MDDB) functionality possible using a traditional relational database. Because relational databases are the most common data management system in organizations today, implementing multi-dimensional views of data using a relational database is very appealing. Even if a specific MDDB solution is used, its sources likely are relational databases. It has been suggested that this article or section be merged with Dimensional database. ... A relational database is a database that conforms to the relational model, and refers to a databases data and schema (the databases structure of how that data is arranged). ...

Another reason for using star schema is its ease of understanding. Fact tables in star schema are mostly in third normal form (3NF), but dimensional tables are in de-normalized second normal form (2NF). If you want to normalize dimensional tables, they look like snowflakes (see snowflake schema) and the same problems of 3NF databases arise - you need complex queries and business users cannot easily understand the meaning of data. Although query performance may be improved by advanced DBMS technology and hardware, highly normalized tables make reporting difficult and applications complex. Database normalization is a series of steps followed to obtain a database design that allows for consistent storage and efficient access of data in a relational database. ... Second normal form (2NF) is a normal form used in database normalization. ... The introduction to this article provides insufficient context for those unfamiliar with the subject matter. ... Database normalization is a series of steps followed to obtain a database design that allows for consistent storage and efficient access of data in a relational database. ... A database management system (DBMS) is a computer program (or more typically, a suite of them) designed to manage a database, a large set of structured data, and run operations on the data requested by numerous users. ...

Example SQL

 SELECT sum (f_sales.units_sold) FROM f_sales, d_customer, d_time, d_store, d_product WHERE f_sales.customer_id = d_customer.customer_id AND f_sales.date_id = d_time.date_id AND f_sales.store_id = d_store.store_id AND f_sales.product_id = d_product.product_id AND d_time.year_id = 1997 AND d_product.category_id = "tv" GROUP BY d_product.brand, d_store.country_iso_id 

Equivalent ANSI SQL-92 Examples

 SELECT sum (f_sales.units_sold) FROM f_sales INNER JOIN d_customer ON d_customer.customer_id = f_sales.customer_id INNER JOIN d_time ON d_time.date_id = f_sales.date_id INNER JOIN d_store ON d_store.store_id = f_sales.store_id INNER JOIN d_product ON d_product.product_id = f_sales.product_id WHERE d_time.year_id = 1997 AND d_product.category_id = "tv" GROUP BY d_product.brand, d_store.country_iso_id 

 SELECT sum (f_sales.units_sold) FROM f_sales INNER JOIN d_customer USING (customer_id) INNER JOIN d_time USING (date_id) INNER JOIN d_store USING (store_id) INNER JOIN d_product USING (product_id) WHERE d_time.year_id = 1997 AND d_product.category_id = "tv" GROUP BY d_product.brand, d_store.country_iso_id 

Alternate ANSI SQL-92 Example

 SELECT sum (f_sales.units_sold) FROM f_sales NATURAL JOIN d_customer NATURAL JOIN d_time NATURAL JOIN d_store NATURAL JOIN d_product WHERE d_time.year_id = 1997 AND d_product.category_id = "tv" GROUP BY d_product.brand, d_store.country_iso_id 

See also

• Snowflake schema

The introduction to this article provides insufficient context for those unfamiliar with the subject matter. ...

External links

• Designing the Star Schema Database by Craig Utley
• Star Schema for Retail Sales
• Stars: A Pattern Language for Query Optimized Schema