What Is Primary Key?
The primary key is the minimum set of traits that distinguishes any row of a table. It cannot have NULL and duplicate values. The primary key is used to add integrity to the table.
In the case of a primary key, both Duplicate and NULL values are not valid. And, it can be utilized as foreign keys for different tables.
What Is a Unique Key?
A unique Key is an individual value that is used to protect duplicate values in a column. The foremost purpose of a unique key in a table is to prevent duplicate values. However, when it comes to a unique value, the primary key also includes it. So, there is one big difference that makes a unique key different, and it is: a unique key can have a NULL value which is not supported in a primary key.
Difference Between Primary Key and Unique Key
|Parameters||Primary Key||Unique Key|
|Basic||The primary key is accepted as a unique or sole identifier for every record in the table.||When the primary key is not present in the table, then the unique key is also used as a unique identifier for records|
|NULL||In the case of a primary key, we cannot save NULL values.||In the case of a unique key, we can save a null value, however, only one NULL value is supported.|
|Purpose||It supports entity integrity.||It supports unique data.|
|Index||The primary key tends to generate a clustered index by default.||The unique key tends to generate a non-clustered index.|
|Number of Key||Each table holds just one primary key.||A table can hold more than one unique key.|
|Value Modification||With the primary key, we cannot modify or delete the values.||With the unique key, we can modify the column values.|
|Uses||It is used to recognize specific records in the table.||It anticipates storing duplicate entries in a column except for a NULL value.|
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