Explanations to questions 3 and 4 are inconsistent?
The explanation to question 3 is that UNIQUE allows us to put just one NULL value. Then, the answer to question 4 should be that we cannot add a record with another NULL value for ID, because the ID must be unique! Why the correct answer to question 4 is another one, instead? Thank you
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Hi Alessandro!
Thanks for reaching out.
Could you please explain which exercises do you refer to? Thank you.
Looking forward to your answer.
Best,
Tsvetelin
Good morning. I refer to "Practice Exam: 1" at the end of chapter 9. The explanation to question 3 says "the former allows us to put only one NULL value", and it refers to UNIQUE keys. Is the explanation to question 3 wrong or is the answer to question 4 wrong? I guess it's the former. Thank you