DBMS -KYES

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Key has important role in relational database: It is used for identifying unique rows from table.It  establishes relationship among tables.

Types of keys :Composite keys ,Super keys , candidate keys, primary key, secondary keys ,

Composite Key : A key that consists of more than one attribute to uniquely identify rows (also known as records & tuples) in a table is called composite key.

Super Key : A super key is a set of one of more attributes to uniquely identify rows in a table.

Candidate Key : A minimal  super key with no redundant attributes .

Primary key: A Primary key is selected from a set of candidate keys. This is done by database admin or database designer. 

Foreign Key : Foreign keys are the attributes of a table that points to the primary key of another table.They act as a cross-reference between tables.


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