Answer
Define the term unique key and give an example.
In databases, a unique key is a column whose values identify one and only one row. People in the United States have a unique key that identifies them: their Social Security number. Everyone has a unique Social Security number which relates only to them, does not change, and is not assigned to anyone else. Another example is books, which have a unique key that identifies them: their ISBN number.
Example: TEXTBOOK (ISBN, Title, Publisher, Copyright) In this row, the ISBN number is a unique key which identifies only one particular book.
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