Primary key in SQL

A primary key is a one-column or combination of the column with a unique value for each row or tuple. The value of the primary key must be unique within the table. The purpose is to bind data together, across tables, without repeating all of the data in every table. It enforces two restrictions on the column - First is Unique value and second is Not null A primary key is the candidate key that is selected to uniquely identify a tuple in a relation. The mandatory and desired attributes...
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