What is a star schema vs snowflake schema?

Star schema is a data warehouse design with a central fact table (containing measurable events like sales transactions) surrounded by dimension tables (descriptive attributes like product, customer, date). Dimension tables are denormalized for query simplicity. Queries are fast with fewer JOINs. Snowflake schema is a more normalized star schema — dimension tables are split into sub-dimensions (e.g., product → category → department). Snowflake reduces storage redundancy but requires more JOINs, making queries more complex. Star schema is preferred for most data warehouses for query performance; snowflake for storage efficiency and strict data integrity.