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Which of the following statement is true?
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- A Primary key is also a candidate key
- Each relation has at least one foreign key
- Foreign keys can’t have null values
- A Primary key is also an alternate key
Correct Option: A
Primary Key is a column or a combination of columns that uniquely identify a record. Only one Candidate Key can be Primary Key. For a Candidate Key to qualify as a Primary Key, it should be unique and non-null. So, basically a primary key is just one of the candidate keys, which is a just a minimal super key.
