First normal form

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First normal form (1NF) is the simplest form of database normalization defined by English computer scientist Edgar F. Codd, the inventor of the relational database. A relation (or a table, in SQL) can be said to be in first normal form if each field is atomic, containing a single value rather than a set of values or a nested table. In other words, a relation complies with first normal form if no attribute domain (the set of values allowed in a given column) has relations as elements.^[1]

Most relational database management systems, including standard SQL, do not support creating or using table-valued columns, which means most relational databases will be in first normal form by necessity. Otherwise, normalization to 1NF involves eliminating nested relations by breaking them up into separate relations associated with each other using foreign keys.^[2]: 381 This process is a necessary step when moving data from a non-relational (or NoSQL) database, such as one using a hierarchical or document-oriented model, to a relational database.

A database must satisfy 1NF to satisfy further "normal forms", such as 2NF and 3NF, which enable the reduction of redundancy and anomalies. Other benefits of adopting 1NF include the introduction of increased data independence and flexibility (including features like many-to-many relationships) and simplification of the relational algebra and query language necessary to describe operations on the database.

Codd considered 1NF mandatory for relational databases, while the other normal forms were merely guidelines for database design.^[3]: 439