database - flattened out vs. normalized

what do they mean when a database is “flattened out” vs. normalized?

2 Answers

"Flattened out" typically refers to a database where you have one (or a few) very large tables.

"Normalized" refers to whether the data has been organized into well-structured, related tables. This typically reduces duplication of values across rows in a table by pulling the values into a separate table and relating to it by ID.

For details, see Database Normalization.

A normalized database is one that is organized to minimize redundancy of data and to produce small and well structured relationships, normally via related tables. An example might be a customer and all his/her orders. In a normalized database, you would have at least two (and probably more) tables. A customer table and an orders table, joined together in some fashion. In a flattened structure, customer and order data might be in a single table.

Reporting databases tend to be denormalized to allows quicker retrieval of data (where many joins may be required), whereas production or transactional databases (OLTP) tend to be (or should be) more normalized with foreign keys established between tables.