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Snowflake schema used by example query. The example schema shown to the right is a snowflaked version of the star schema example provided in the star schema article. The following example query is the snowflake schema equivalent of the star schema example code which returns the total number of television units sold by brand and by country for 1997.
Snowflake IDs, or snowflakes, are a form of unique identifier used in distributed computing. The format was created by Twitter (now X) and is used for the IDs of tweets. [ 1 ] It is popularly believed that every snowflake has a unique structure, so they took the name "snowflake ID".
Example of a star schema; the central table is the fact table. In data warehousing, a fact table consists of the measurements, metrics or facts of a business process. It is located at the center of a star schema or a snowflake schema surrounded by dimension tables. Where multiple fact tables are used, these are arranged as a fact constellation ...
The star schema consists of one or more fact tables referencing any number of dimension tables. The star schema is an important special case of the snowflake schema, and is more effective for handling simpler queries. [2]
The date dimension primary key could be a surrogate key or a number using the format YYYYMMDD. The date dimension can include other attributes like the week of the year, or flags representing work days, holidays, etc. It could also include special rows representing: not known dates, or yet to be defined dates.
These dimensions are where all the data is stored. For example, the date dimension could contain data such as year, month and weekday. Identify the facts. After defining the dimensions, the next step in the process is to make keys for the fact table. This step is to identify the numeric facts that will populate each fact table row.
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Examples of column-oriented formats include Apache ORC, [3] Apache Parquet, [4] Apache Arrow, [5] formats used by BigQuery, Amazon Redshift and Snowflake. Predominant examples of row-oriented formats include CSV, formats used in most relational databases , the in-memory format of Apache Spark , and Apache Avro .