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Difference Between Primary and Candidate Key
In this post, we will understand the difference between primary key and the candidate key.
Primary Key
It is used to ensure that the data in the specific column is unique.
It helps uniquely identify a record in a relational database.
One primary key only is allowed in a table.
It is a combination of the ‘UNIQUE’ and ‘Not Null’ constraints.
This means it can’t be a NULL value.
It is the most important part of a table.
It is a candidate key.
Its value can’t be deleted from parent table.
The constraint can be implicitly defined for the temporary tables.
Candidate key
It can have NULL value.
It may or may not have a primary key.
It tells about which key can be used as a primary key.
It is a unique key that helps identify a record uniquely in a table.
A table can have multiple candidate keys.
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