Learn SQL: Primary Key

What is a Primary Key? - Definition from WhatIs.com

Definition of primary key

Foreign Key vs Primary Key - What is the Difference? - Essential SQL

What Is a Primary Key? | IBM

Q1.Answer the following:(10)a. Is it mandatory for a foreign key to be a primary key in another table?b. Can foreign keys be null values in child relation?c. After enforcing foreign key constraint using on delete cascade rule, can you delete therecord in the child relation whose foreign key is not null before deleting the record in theparent relation?d. Can foreign keys have the duplicate values?e. Can there exist more than one foreign key in relation?Q2. Create fully normalized ERDs with primar

SQL Foreign key

Definition of foreign key