Please checkout the below details Primary Key
- Primary key cannot have a NULL value.
- Each table can have only one primary key.
- By default, Primary key is clustered index and data in the database table is physically organized in the sequence of clustered index.
- Primary key can be related with another table’s as a Foreign Key.
- We can generated ID automatically with the help of Auto Increment field. Primary key supports Auto Increment value.
- Foreign key is a field in the table that is primary key in another table.
- Foreign key can accept multiple null value.
- Foreign key do not automatically create an index, clustered or non-clustered. You can manually create an index on foreign key.
- We can have more than one foreign key in a table.
- Foreign keys do not automatically create an index, clustered or non-clustered. You must manually create an index on foreign keys.
- Unique Constraint may have a NULL value.
- Each table can have more than one Unique Constraint.
- By default, Unique key is a unique non-clustered index.
- Unique Constraint can not be related with another table’s as a Foreign Key.
- Unique Constraint doesn’t supports Auto Increment value.