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Q: Which of the following statement is true?
  • A. A Primary key is also a candidate key
  • B. Each relation has at least one foreign key
  • C. Foreign keys can't have null values
  • D. A Primary key is also an alternate key
Correct Answer: Option A - A database is used to store the information of an organization. We use the principles of the key to create these database. There are mainly 4 types- Primary key, Foreign key, Candidate key and Alternate key. Someone who can fulfill all the requirements of the "Primary Key" to preserve a record, it is also called "Candidate key".
A. A database is used to store the information of an organization. We use the principles of the key to create these database. There are mainly 4 types- Primary key, Foreign key, Candidate key and Alternate key. Someone who can fulfill all the requirements of the "Primary Key" to preserve a record, it is also called "Candidate key".

Explanations:

A database is used to store the information of an organization. We use the principles of the key to create these database. There are mainly 4 types- Primary key, Foreign key, Candidate key and Alternate key. Someone who can fulfill all the requirements of the "Primary Key" to preserve a record, it is also called "Candidate key".