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A key

This question belongs to Database The Relational Model And Normalization
The Relational Model and Normalization
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A key:

Answer & Solution
Correct Answer: Option C
Option1: A key must always be composed of two or more columns because a composite key is used to uniquely identify a row in a table when a single column key is not sufficient.
Option2: A key can only be one column is incorrect because a key can be composed of multiple columns to uniquely identify a row in a table.
Option3: A key identifies a row is correct. A key is used to uniquely identify a row in a table and ensure that each row is unique.
Option4: A key identifies a column is incorrect. A key is used to identify a row, not a column in a table.
In conclusion, the correct option is Option3: identifies a row. A key is used to uniquely identify a row in a table and ensure data integrity.
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