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:
Select the option that expresses the given sentence in indirect speech.
“How beautiful she is!” said Betty.
Choose the correct indirect/direct speech which best expresses the following sentence:- He said, "I was writing an application to the mayor about pathet...
Select the correct Direct / Indirect form of the given sentence.
Radha told me, "please send my mobile".
Select the most appropriate indirect form of the given sentence.
Frank said to Albert, “ How is your search for a new house coming along?”
Select the option which correctly converts the given sentence into direct speech.
He exclaimed with regret that he had behaved very rudely with h...
Select the option that expresses the given sentence in direct speech.
She told the villagers that she would not rest till she had solved their wa...
Choose the option that is the indirect form of the sentence.
“I’m hungry” said the child to his mother.
The child said, "What a beautiful sight!"
Select the most appropriate indirect form of the given sentence.
I said to Promod, “How did you break your leg?”
I said to the old man, "Don't sit on that chair, it is broken."