correct way of primary key and foreign key code example

Example 1: difference primary key and foreign key

Primary Key :
It is unique column in every table in a database
It can ONLY accept;
    - nonduplicate values
    - cannot be NULL
Foreign Key: 
It is a column that comes from a different table and
using Foreign key tables are related each other
It is the primary key of another table
It can be duplicate or null for another table

Unique Key:
Only unique value and also can contain NULL

Example 2: What is foreign key?

Foreign Key is a non-key attribute which is derived from the primary key 
of another table which links those tables together.

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Sql Example

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