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In the relational model of databases, a primary key is a designated attribute that can reliably identify and distinguish between each individual record in a table.The database creator can choose an existing unique attribute or combination of attributes from the table (a natural key) to act as its primary key, or create a new attribute containing a unique ID that exists solely for this purpose ...
A key that may become the primary key. Primary The key that is selected as the primary key. Only one key within an entity is selected to be the primary key. This is the key that is allowed to migrate to other entities to define the relationships that exist among the entities.
A requirement of E. F. Codd in his seminal paper is that a primary key of an entity, or any part of it, can never take a null value. [1] The relational model states that every relation (or table ) must have an identifier, called the primary key (abbreviated PK), in such a way that every row of the same relation be identifiable by its content ...
A candidate key, or simply a key, of a relational database is any set of columns that have a unique combination of values in each row, with the additional constraint that removing any column could produce duplicate combinations of values. A candidate key is a minimal superkey, [1] i.e., a superkey that doesn't contain a smaller one. Therefore ...
A foreign key is a set of attributes in a table that refers to the primary key of another table, linking these two tables. In the context of relational databases, a foreign key is subject to an inclusion dependency constraint that the tuples consisting of the foreign key attributes in one relation, R, must also exist in some other (not necessarily distinct) relation, S; furthermore that those ...
The Keys to the White House, also known as the 13 keys, is a prediction system for determining the outcome of presidential elections in the United States.It was developed by American historian Allan Lichtman and Russian geophysicist Vladimir Keilis-Borok in 1981, adapting methods that Keilis-Borok designed for earthquake prediction.
Material based on primary sources can be valuable and appropriate additions to Wikipedia articles, but only in the form of straightforward descriptive statements that any educated person—with access to the source but without specialist knowledge—will be able to verify are directly supported by the source. This person does not have to be ...
While an overall database key article is useful (and Key (database) is a better name than unique key), "primary key" is a common term, and deserves its own article. Many of the comments at Talk:Unique key ask for clarification on what a primary key is, and how it differs from a unique key.