GATE CSE 2019 | Question: 51

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GATE CSE 2019 | Question: 51

Arjun asked Feb 7, 2019 • retagged Nov 30, 2022 by Lakshman Bhaiya

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A relational database contains two tables Student and Performance as shown below:

$$\overset{\text{Table: student}}{\begin{array}{|l|l|} \hline \text{Roll_no} & \text{Student_name}\\\hline 1 & \text{Amit} \\\hline 2 & \text{Priya} \\\hline 3 & \text{Vinit} \\\hline 4 & \text{Rohan} \\\hline 5 & \text{Smita} \\\hline \end{array}} \qquad\overset{\text{Table: Performance}}{\begin{array}{|l|l|l|} \hline \text{Roll_no} & \text{Subject_code} & \text{Marks}\\\hline 1 & \text{A} & 86 \\\hline 1 & \text{B} & 95 \\\hline 1 & \text{C} & 90 \\\hline 2 & \text{A} & 89 \\\hline 2 & \text{C} & 92 \\\hline 3 & \text{C} & 80 \\\hline \end{array}}$$

The primary key of the Student table is Roll_no. For the performance table, the columns Roll_no. and Subject_code together form the primary key. Consider the SQL query given below:

SELECT S.Student_name, sum(P.Marks) 
FROM Student S, Performance P 
WHERE P.Marks >84 
GROUP BY S.Student_name;

The number of rows returned by the above SQL query is ________

Arjun asked Feb 7, 2019 • retagged Nov 30, 2022 by Lakshman Bhaiya

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I think it is 2 , because we needed to show the sum of marks the student got (based on the join condition we choose the student ) and when group by happens only 2 tuples remain .. — Shashi Shekhar 1, Feb 4, 2019
can you share the exact sql query ? I don't remember it , but all I could say is it was 5 — prashant jha 1, Feb 4, 2019
Well I did not remember the exact complete question , therefore pardon me ,I just commented based on whatever I remembered. — Shashi Shekhar 1, Feb 4, 2019
Two roll numbered students marks were to be returned using group by clause.

Answer was 2. — Duffer, Feb 4, 2019
As far as i remember , there was a cross join , and there was a group by , with no other condition. If this is true , then answer would be 5 , I might have missed something , kindly post the problem here if you remember — prashant jha 1, Feb 4, 2019
SELECT s.student_name, sum(p.marks)
FROM student s, performance P
WHERE p.marks>84
GROUP BY s.student.name — Archit, Feb 4, 2019
Yes in my opinion too there was no other join condition specified in the question so all tuples must be selected as the names in the first table mentioned were all distinct. — Archit, Feb 4, 2019
Actually there was roll no in both the tables over which the join would happen , which would result in 5 tuples , 2 for Amit and 3 for Raman(assumed names ),and when group by happens it would result in 2. — Shashi Shekhar 1, Feb 4, 2019
Plz correct me if I am wrong but if some attribute is matching in cross product ,it is natural join by default on those attributes. — Shashi Shekhar 1, Feb 4, 2019
What's the purpose of explicitly mentioning natural join then in queries ? Just give commas and automatically natural join will be done. — prashant jha 1, Feb 4, 2019
SELECT s.student_name, sum(p.marks)
FROM student s, performance P
WHERE p.marks>84
GROUP BY s.student.name

@Sharad Shukla 5 can you tell me what am I missing here? — prashant jha 1, Feb 5, 2019
@Ahabnnc @Deepanshu

What is answer for inherited sttribute ques ??

Q 53

And what is answer for GA question on directions ??

Q7 — jatin khachane 1, Feb 7, 2019
Reenakhanna That is on natural join, here cross product is considered as join condition is not given. — palashbehra5, Nov 7, 2021
But sir,..when written in ques is join and we find two table having same attribute (here is Roll no.) ..then we do natural join . If not,plz explain. — Pj25, Oct 13, 2022
In the link given question there is condition given so it is natural join. But in the given question we consider as cross product.

Hope you understand. — theredeepakb, Nov 12, 2021
@Shaik Masthan sir,
SELECT S.Student_name, sum(P.Marks) -----> 4.Display
FROM Student S, Performance P ------> 1. Cross product
WHERE P.Marks >84 ------> 2. Conditon check
GROUP BY S.Student_name; -----> 3.group By — satyaAchar, Feb 1

Priyansh Kimtee · Answer 1 · 2019-02-07T11:48:07+0000

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Praveenk99 · Answer 2 · 2019-12-19T15:09:42+0000

Remember this basic rule in sql

SELECT= PROJECTION

FROM= CROSS PRODUCT

WHERE= SELECT CONDITION

here in the given query we need to take cross product which returns 25 query with keeping in mind the condition to jave marks > 84 so when we group by our answer would be

Amit 452

Priya 452

Vinit 452

Roshan 452

Smita 452

So 5 tuples

Shashank Mishra · Answer 3 · 2019-02-04T08:03:23+0000

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content	content:apple
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force match	+apple
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