ACorrect Answer

This is true. In such cases the relationship is said to have "optionality".

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BIncorrect Answer

The primary key field may NEVER be null. Don't be so stupid!

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CIncorrect Answer

Third normal form is certainly desirable, however relations which are only in first normal form may be stored in a relational database.

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DIncorrect Answer

Many to many mappings may be represent - usually by introducing an extra table of "pairs".

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EIncorrect Answer

This restriction is not general. Some implementations (notably dBase III) require primary key fields to be adjacent.

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A B C D E TELL ME NEXT INDEX
 
 

Which of the following statements concerning relational databases is true?

  1. A foreign key field may be null.

  2. A primary key field may be null

  3. All relations must be in at least third normal form

  4. Many to many mappings cannot be represented

  5. The primary key fields of a relation must be adjacent