GATE CS 2024 Set 1 — Question 35
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Databases → Relational Model → Joins
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Question
Consider the following two relations,
Relation S
The total number of tuples obtained by evaluating the following expressionis _________
R(A,B) and S(A,C):Relation R| A | B |
|---|---|
| 10 | 20 |
| 20 | 30 |
| 30 | 40 |
| 30 | 50 |
| 50 | 95 |
| A | C |
|---|---|
| 10 | 90 |
| 30 | 45 |
| 40 | 80 |
Correct answer
2 to 2
Solution
To evaluate the expression , we first perform the natural join (equi-join on attribute ) between relations and , and then apply the selection condition .Step 1: Perform the Join ()
We match tuples from and where .
We filter the joined tuples where the value of attribute is strictly less than attribute .
The tuples satisfying the condition are and .Total number of tuples = 2.
We match tuples from and where .
- For : has and has .
- Resulting tuple:
- For : has but has no tuple with . No match.
- For : has and . has .
- Match with
- Match with
- For : has but has no tuple with . No match.
- For : has but has no tuple with . No match.
1.
2.
3.
Step 2: Apply Selection ()We filter the joined tuples where the value of attribute is strictly less than attribute .
1.Tuple : . Is ? Yes.
2.Tuple : . Is ? Yes.
3.Tuple : . Is ? No.
Step 3: Count the TuplesThe tuples satisfying the condition are and .Total number of tuples = 2.
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