What are the difference between Primary Keys and Foreign Keys?

What are the difference between Primary Keys and Foreign Keys?

Primary key:

Primary keys are the unique identifiers for each row. They must contain unique values and cannot be null. Due to their importance in relational databases, Primary keys are the most fundamental aspect of all keys and constraints. A table can have only one primary key.

• The PRIMARY KEY constraint uniquely identifies each record in a database table.
•  Primary keys must contain unique values.
• A primary key column cannot contain NULL values.
•   Each table should have a primary key, and each table can have only ONE primary key.

Foreign key:

Foreign keys are a method of ensuring data integrity and manifestation of the relationship between tables. A FOREIGN KEY in one table points to a PRIMARY KEY in another table.

Difference between Primary Key & Foreign Key:

Primary Key	Foreign Key
Primary key uniquely identify a record in the table.	Foreign key is a field in the table that is primary key in another table.
Primary Key can't accept null values.	Foreign key can accept multiple null value.
By default, Primary key is clustered index and data in the database table is physically organized in the sequence of clustered index.	Foreign key do not automatically create an index, clustered or non-clustered. You can manually create an index on foreign key.
We can have only one Primary key in a table.	We can have more than one foreign key in a table.