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What is true about Unique and primary key?(a) Unique can have multiple NULL values but Primary can’t have.(b) Unique can have single NULL value but Primary can’t have even single.(c) Both can have duplicate values(d) None of the MentionedThe question was posed to me in homework.My doubt stems from Foreign, Candidate, Primary, Composite, Unique Keys topic in section Planning Oracle Applications of Oracle |
Answer» <html><body><p>Right <a href="https://interviewquestions.tuteehub.com/tag/option-25810" style="font-weight:bold;" target="_blank" title="Click to know more about OPTION">OPTION</a> is (b) <a href="https://interviewquestions.tuteehub.com/tag/unique-720618" style="font-weight:bold;" target="_blank" title="Click to know more about UNIQUE">UNIQUE</a> can have single NULL value but Primary can’t have even single.<br/><br/>To <a href="https://interviewquestions.tuteehub.com/tag/explain-447165" style="font-weight:bold;" target="_blank" title="Click to know more about EXPLAIN">EXPLAIN</a> I would <a href="https://interviewquestions.tuteehub.com/tag/say-1195451" style="font-weight:bold;" target="_blank" title="Click to know more about SAY">SAY</a>: Primary key doesn’t allow Null values and Unique key allows Null value, but only <a href="https://interviewquestions.tuteehub.com/tag/one-585732" style="font-weight:bold;" target="_blank" title="Click to know more about ONE">ONE</a> Null value.</p></body></html> | |