Java notes part 1

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Types of SQL Keys

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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