In the Employee table, the Employee_id of all employees are different . So it can be used to uniquely identify each employee and hence, we set Employee_id as the primary key.

Additional points:

A relation can have only 1 primary key.
A primary key can consist of single or multiple columns.
Primary keys must contain unique values.
Primary keys cannot contain NULL values.

Transcript

What is primary key? Answer: Primary key is a set of one or more attributes which can uniquely identify each tuple of a relation. Example: Employee_id Employee_name Department 101 Ravi Kumar Sales 102 Tarun A IT 103 Jennifer Davis HR 104 Martin Woods HR 105 Ron Romy IT In the Employee table, the Employee_id of all employees are different. So it can be used to uniquely identify each employee and hence, we set Employee_id as the primary key. Additional points: A relation can have only 1 primary key. A primary key can consist of single or multiple columns. Primary keys must contain unique values. Primary keys cannot contain NULL values.

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Davneet Singh

Davneet Singh has done his B.Tech from Indian Institute of Technology, Kanpur. He has been teaching from the past 14 years. He provides courses for Maths, Science, Social Science, Physics, Chemistry, Computer Science at Teachoo.

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