Question

what is primary key?
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Answer 1

Answer:

In the relational model of databases, a primary key is a specific choice of a minimal set of attributes that uniquely specify a tuple in a relation. Informally, a primary key is "which attributes identify a record", and in simple cases are simply a single attribute: a unique id.

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Answer 2

Answer:

In the relational model of databases, a primary key is a specific choice of a minimal set of attributes (columns) that uniquely specify a tuple (row) in a relation (table).[a][1] Informally, a primary key is "which attributes identify a record", and in simple cases are simply a single attribute: a unique id. More formally, a primary key is a choice of candidate key (a minimal superkey); any other candidate key is an alternate key.

A primary key may consist of real-world observables, in which case it is called a natural key, while an attribute created to function as a key and not used for identification outside the database is called a surrogate key. For example, for a database of people (of a given nationality), time and location of birth could be a natural key.[b] National identification number is another example of an attribute that may be used as a natural key.

Explanation:

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