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Candidate key - RDBMS Foreign key - RDBMS
Primary key - RDBMS - SQL
72    Arnab De    21/11/2021   

Primary Keyis an unique attribute or set of unique attributes that can uniquely identify a tuple in a relation.

Primary key is auniqueandnot null attribute in a tuple. i.e. we cannot insert a tuple with blank or duplicate value in a primary key attribute.

Lets consider, a relation called emp

Emp
Emp_SSN Emp_No Emp_Name
1234544434 E-001 Pradipta Pal
5345232444 E-002 Abhijit Ganguly
4645673422 E-003 Suman Banerjee
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In the above relation called (Emp), Emp_SSN is a Primary Key. Here every Emp_SSN is unique and not null.

A Primary key is selected from a set of candidate keys. This is done by database admin or database designer. We can say that either {Emp_SSN} or {Emp_Number} can be chosen as a primary key for the table Employee.

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Candidate key - RDBMS Foreign key - RDBMS
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Author Details
Arnab De
I have over 16 years of experience working as an IT professional, ranging from teaching at my own institute to being a computer faculty at different leading institute across Kolkata. I also work as a web developer and designer, having worked for renowned companies and brand. Through tutorialathome, I wish to share my years of knowledge with the readers.
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