DBMS -KYES
Key has important role in relational database: I t 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 .