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A candidate key is a minimal superkey that uniquely identifies tuples in a relation. A fundamental property of candidate keys is that they cannot contain NULL values. This is because NULL signifies "unknown" or "not applicable," and allowing NULL values in a candidate key would mean that we cannot guarantee the uniqueness of the key. If a candidate key were allowed to have NULL values, there could be ambiguity in identifying records, which violates the principle of uniqueness and reliability. For example, if two tuples share the same key attributes except for one containing a NULL, the database cannot assert the uniqueness of these tuples. Why Other Options Are Incorrect:
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Profit percentage received on a product when sold for Rs.550 is equal to the percentage loss incurred when the same product is sold for Rs.380. Find the...
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A man sells two articles at 29.180 each. He gains 8% on one article and loses 15% on the other. His overall profit or loss is:
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