Stanford Online Course Relational Algebra - Set Difference Operator
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Problem: Consider a relation R(A) with r tuples, all unique within R, and a relation S(A) with s tuples, all unique within S. Let t represent the number of tuples in R minus S. Which of the following triples of values (r,s,t) is possible?
Potential Answers:
(10,13,8)
(5,3,1)
(5,0,3)
(8,2,2)
I tried to solve this on my own by creating 2 example tables with R(A) and S(A). I know with bag difference, an element appears in the difference A-B of bags as many times as it appears in A, minus the number of times it appears in B. But never less than 0 times.
Example:
Relation R
| A |
|---|
| 1 |
| 2 |
| 3 |
| 4 |
Relation S
| A |
|---|
| 4 |
| 5 |
| 6 |
| 7 |
If I do R - S I get the following result 1, 2, 3.
Couldn't it be any of the potential answers (Except '5,0,3') since the amount of tuples just has to be less than the number of tuples in A or B?
relation-algebra
asked Dec 4 '18 at 22:42
Maggie LiuMaggie Liu
11
$endgroup$
add a comment |
$begingroup$
Problem: Consider a relation R(A) with r tuples, all unique within R, and a relation S(A) with s tuples, all unique within S. Let t represent the number of tuples in R minus S. Which of the following triples of values (r,s,t) is possible?
Potential Answers:
(10,13,8)
(5,3,1)
(5,0,3)
(8,2,2)
I tried to solve this on my own by creating 2 example tables with R(A) and S(A). I know with bag difference, an element appears in the difference A-B of bags as many times as it appears in A, minus the number of times it appears in B. But never less than 0 times.
Example:
Relation R
| A |
|---|
| 1 |
| 2 |
| 3 |
| 4 |
Relation S
| A |
|---|
| 4 |
| 5 |
| 6 |
| 7 |
If I do R - S I get the following result 1, 2, 3.
Couldn't it be any of the potential answers (Except '5,0,3') since the amount of tuples just has to be less than the number of tuples in A or B?
relation-algebra
asked Dec 4 '18 at 22:42
Maggie LiuMaggie Liu
11
$endgroup$
add a comment |
$begingroup$
Problem: Consider a relation R(A) with r tuples, all unique within R, and a relation S(A) with s tuples, all unique within S. Let t represent the number of tuples in R minus S. Which of the following triples of values (r,s,t) is possible?
Potential Answers:
(10,13,8)
(5,3,1)
(5,0,3)
(8,2,2)
I tried to solve this on my own by creating 2 example tables with R(A) and S(A). I know with bag difference, an element appears in the difference A-B of bags as many times as it appears in A, minus the number of times it appears in B. But never less than 0 times.
Example:
Relation R
| A |
|---|
| 1 |
| 2 |
| 3 |
| 4 |
Relation S
| A |
|---|
| 4 |
| 5 |
| 6 |
| 7 |
If I do R - S I get the following result 1, 2, 3.
Couldn't it be any of the potential answers (Except '5,0,3') since the amount of tuples just has to be less than the number of tuples in A or B?
relation-algebra
asked Dec 4 '18 at 22:42
Maggie LiuMaggie Liu
11
$endgroup$
Problem: Consider a relation R(A) with r tuples, all unique within R, and a relation S(A) with s tuples, all unique within S. Let t represent the number of tuples in R minus S. Which of the following triples of values (r,s,t) is possible?
Potential Answers:
(10,13,8)
(5,3,1)
(5,0,3)
(8,2,2)
I tried to solve this on my own by creating 2 example tables with R(A) and S(A). I know with bag difference, an element appears in the difference A-B of bags as many times as it appears in A, minus the number of times it appears in B. But never less than 0 times.
Example:
Relation R
| A |
|---|
| 1 |
| 2 |
| 3 |
| 4 |
Relation S
| A |
|---|
| 4 |
| 5 |
| 6 |
| 7 |
If I do R - S I get the following result 1, 2, 3.
Couldn't it be any of the potential answers (Except '5,0,3') since the amount of tuples just has to be less than the number of tuples in A or B?
relation-algebra
relation-algebra
asked Dec 4 '18 at 22:42
Maggie LiuMaggie Liu
11
asked Dec 4 '18 at 22:42
Maggie LiuMaggie Liu
11
asked Dec 4 '18 at 22:42
Maggie LiuMaggie Liu
11
asked Dec 4 '18 at 22:42
Maggie LiuMaggie Liu
11
asked Dec 4 '18 at 22:42
Maggie LiuMaggie Liu
11
11
add a comment |
add a comment |
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