What is a Key? What are different types of Keys in a database? Answer: A key is nothing but an attribute or group of attributes. Attribute is a particular property, which describes the entity. Attributes are also called columns or fields in DBMS. Keys are used to establish and identify relation between tables. They also ensure that each record within a table can be uniquely identified by combination of one or more fields within a table. Different types of keys in database are primary key, secondary key, alternative key, super key, candidate key, compound or concatenated or composite key, foreign key, etc. What is a Primary Key? Answer: An attribute that can be used to identify a record uniquely is considered to be a Primary Key. For example, In the student table roll_no is the primary key because it can be used to identify unique record or unique student. What is a Secondary Key? Answer: An attribute that can be used to identify a group of records satisfying a give...
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