1. The relation R(a,b) may have duplicate tuples. Which of the following queries

Question

1.   The relation R(a,b) may have duplicate tuples. Which of the following queries has a result that is guaranteed not to have duplicates, regardless of what tuples R contains? a) SELECT a, AVG(b) FROM R GROUP BY a b) SELECT b FROM R WHERE a = b c) SELECT a FROM R WHERE a >= ALL (SELECT a FROM R) d) SELECT a FROM R WHERE a = 1 2.   Relation R(a,b) has no duplicate tuples, although neither a nor b is a key. Relation S(c,d) may have duplicates. Which of the following queries is guaranteed to produce no duplicates? a) SELECT c, d FROM S WHERE c IN (SELECT a FROM R) AND d IN (SELECT b FROM R) b) SELECT S.c, S.d FROM R, S WHERE R.a = S.d AND R.b = S.c c) SELECT c FROM S WHERE c = d d) SELECT c, d FROM S GROUP BY c, d 1.   The relation R(a,b) may have duplicate tuples. Which of the following queries has a result that is guaranteed not to have duplicates, regardless of what tuples R contains?

Explanation / Answer

1)Answer:

Here you have given that

the relation R(a,b) may have duplicate tuples.

SO for getting the result that is guaranteed not to have duplicates

SELECT a FROM R WHERE a = 1

2)Answer:

Given that Relation R(a,b) has no duplicate tuples and a nor b is a key

and we have Relation S(c,d) may have duplicates

So that

SELECT S.c, S.d FROM R, S WHERE R.a = S.d AND R.b = S.c

Hope this will helps you...

Related Questions

Navigate

• Browse (All)
• Browse 1
• Subjects

---

---

Integrity-first tutoring: explanations and feedback only — we do not complete graded work. Learn more.