Question

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Write about primary key .......

Answer 1

In the relational model of databases, a primary key is a specific choice of a minimalset of attributes (columns) that uniquely specify a tuple (row) in a relation (table).[a]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 is called a surrogate key. For example, for a database of people (of a given nationality), time and location of birth is a natural key,[b] while national identification numbers are surrogate keys.



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Answer 2

Here is your answer
A primary key, also called a primary keyword, is a key in a relational database that is unique for each record. It is a unique identifier, such as a driver license number, telephone number (including area code), or vehicle identification number (VIN). A relational database must always have one and only one primary key. Primary keys typically appear as columns in relational database tables.