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We have following types of keys in SQL which are used to fetch records from tables and to make relationship among tables or views. Super Key Super key is a set of one or more than one keys that can be used to identify a record uniquely in a table. Example : Primary key, Unique key, Alternate key are subset of Super Keys. Candidate Key A Candidate Key is a set of one or more fields/columns that can identify a record uniquely in a table. There can be multiple Candidate Keys in one table. Each Candidate Key can work as Primary Key. Primary Key Primary key is a set of one or more fields/columns of a table that uniquely identify arecord in database table. It can not accept null, duplicate values. Only one Candidate Key can be Primary Key. Alternate key A Alternate key is a key that can be work as a primary key. Basically it is a candidate key that currently is not primary key. Composite/Compound Key Composite Key is a combin...
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