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Primary Key
Unique Key
Primary Key can’t accept null values.
Unique key can accept only one null value.
By default, Primary key is clustered index
and data in the database table is physically
organized in the sequence of clustered index.
and data in the database table is physically
organized in the sequence of clustered index.
By default, Unique key is a unique non-clustered index.
We can have only one Primary key in a table.
We can have more than one unique key in a table.
Primary key can be made foreign key into another table.
In SQL Server, Unique key can be made foreign key into another table.
Example:
Create table Student
(
StuId int primary key, —- Define Primary Key
StuName varchar(50) Not Null,
ContactNo int Unique — Define Unique Key
)
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