Home > Star schema
The star schema (sometimes referenced as star join schema) is the simplest data warehouse schema where a single " fact table " containing a compound primary key, with one segment for each "dimension" and additional columns of additive, numeric facts.The start schema makes multi-dimensional database(MDDB) possible within relational database. Beacause relational database is the basic data management system in most organization today, it is very appealing that multi-dimensional view of data is implemented in relational database. Even if you are using a specific MDDB solution, its sources are relational databases. Another reason for using star schema is its ease of understanding. Fact tables in star schema is mostly in 3NF, but dimensional tables in de-normalized 2NF. If you want to normalize dimensional tables, they look like snowflakes and the
same problems of relational database 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 application complex.
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
GROUP BY
d_store.country_iso_id
Data management
