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A candidate key (or minimal superkey) is a superkey that can't be reduced to a simpler superkey by removing an attribute. [ 3 ] For example, in an employee schema with attributes employeeID , name , job , and departmentID , if employeeID values are unique then employeeID combined with any or all of the other attributes can uniquely identify ...
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 ...
However, only S 1, S 2, S 3 and S 4 are candidate keys (that is, minimal superkeys for that relation) because e.g. S 1 ⊂ S 5, so S 5 cannot be a candidate key. Given that 2NF prohibits partial functional dependencies of non-prime attributes (i.e., an attribute that does not occur in any candidate key ) and that 3NF prohibits transitive ...
At the most basic definition, "a key is a unique identifier", [1] so unique key is a pleonasm. Keys that are within their originating entity are unique within that entity. Keys that migrate to another entity may or may not be unique, depending on the design and how they are used in the other table.
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 ...
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Super key may refer to: Super key (keyboard button), modifier key on keyboards; Superkey, database relation This page was last edited on 14 ...
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