The unique key or primary key of the table referenced by a foreign key.

Primary Key, Foreign Key, Relationship Type, Referential Integrity.

If no primary key is defined MySQL will use first unique key as primary key if there is one.

Ans: Primary Key – Primary key is one of the candidate keys.

Set the primary key using the instructions in the section Set the primary key.

Composite key is a primary key that consists of two or more attributes.

Composite key:- A primary key that consists of two or more attributes is known as

Differences Between a Primary Key and a Unique Key

The key holes (4, 6) are respectively a main key hole (4) and a secondary key hole (6).

Key Differences Between Primary key and Unique key

A foreign key is any attribute that is nonkey in one relation but a primary key in another relation.

Set the primary key using the instructions in the section Set the primary key.

Remove the existing primary key using the instructions in the section Remove the primary key.

The columns must be in a primary key/foreign key relationship.

Remove the existing primary key using the instructions in the section Remove the primary key.