1NF - определение. Что такое 1NF
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Что (кто) такое 1NF - определение

MINIMUM REQUIREMENT IN DATABASE NORMALIZATION
1NF; 1st normal form; Repeating group

1NF         
first normal form         
repeating group         
<database> Any attribute that can have multiple values associated with a single instance of some entity. For example, a book might have multiple authors. Such a "-to-many" relationship might be represented in an unnormalised relational database as multiple author columns in the book table or a single author(s) column containing a string which was a list of authors. Converting this to "first normal form" is the first step in database normalisation. Each author of the book would appear in a separate row along with the book's primary key. Later nomalisation stages would move the book-author relationship into a separate table to avoid repeating other book attibutes (e.g. title, publisher) for each author. (2005-07-28)

Википедия

First normal form

First normal form (1NF) is a property of a relation in a relational database. A relation is in first normal form if and only if no attribute domain has relations as elements. Or more informally, that no table column can have tables as values (or no repeating groups). Database normalization is the process of representing a database in terms of relations in standard normal forms, where first normal is a minimal requirement. SQL-92 does not support creating or using table-valued columns, which means that using only the "traditional relational database features" (excluding extensions even if they were later standardized) most relational databases will be in first normal form by necessity. Database systems which do not require first normal form are often called NoSQL systems. Newer SQL standards like SQL:1999 have started to allow so called non-atomic types, which include composite types. Even newer versions like SQL:2016 allow JSON.