Answers for "difference between primary key and foreign"

primary key vs 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

foreign key and primary key difference

PrimaryKey:-

A primary key constrain is a column or group of columns that uniquely identifies every row in the table of the relational database management system. 
It cannot be a duplicate, meaning the same value should not appear more than once in the table.

Foreign key:-
A table can have more than one primary key. 
Primary key can be defined at the column or the table level.
If you create a composite primary key, it should be defined at the table level.
Foreign key is a column that creates a relationship between two tables. The purpose of the Foreign key is to maintain data integrity and allow navigation between two different instances of an entity. It acts as a cross-reference between two tables as it references the primary key of another table. 
Every relationship in the database should be supported by a foreign key.