UGC NET CSE | December 2018 | Part 2 | Question: 84

Question

Consider the following tables (relations):

Students
Roll-No	Name
18CS101	Ramesh
18CS102	Mukesh
18CS103	Ramesh

 

Performance
Roll-No	Course	Marks
18CS101	DBMS	60
18CS101	Compiler Design	65
18CS102	DBMS	80
18CS103	DBMS	85
18CS102	Compiler Design	75
18CS103	Operating System	70

 

Primary keys in the tables are shown using underline. Now, consider the following query:

SELECT S.Name, Sum (P.Marks) FROM Students, Performance P WHERE S.Roll-No=P.Roll-No GROUP BY S.Name

The number of rows returned by the above query is

• A. $0$
• B. $1$
• C. $2$
• D. $3$

Comments

It will return 2 rows

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2 rows

Answer 1

Answer is (C) 2

The Below Query will return 2 rows

SELECT S.Name, Sum (P.Marks)as Marks FROM Students, Performance P WHERE S.Roll-No=P.Roll-No GROUP BY S.Name

Since, Here Grouping is on S.Name

So, Output will be as below

Name         Marks

Ramesh      280

Mukesh      155

If the query will be as below then we get 3 rows

SELECT S.Roll-No, S.Name, Sum (P.Marks) as Marks FROM Students, Performance P WHERE S.Roll-No=P.Roll-No GROUP BY S.Roll-No, S.Name

Output of the above query by using the given tables in the question output will be as below

Roll-No                Name                Marks

18CS101            Ramesh              125

18CS102            Mukesh              155

18CS103           Ramesh              155