Gate2017 cs Q63

0. Consider a database that has the relation schema CR (StudentName, CourseName). An instance of the schema CR is as given below.
CR
Student Name Course Name
SA CA
SA CB
SA CC
SB CB
SB CC
SC CA
SC CB
SC CC
SD CA
SD CB
SD CC
SD CD
SE CD
SE CA
SE CB
SF CA
SF CB
SF CC
The following query is made on the database.

T1 ← π_CourseName(σ_{StudentName=’SA’}(CR))

T2 ← CR ÷ T1
The number of rows in T2 is ________.

Note – Numerical Type question

Answer
Comment
Array

Option : C
Explanation :
Explanation: Result of T1:
CA
CB
CC

Result of T2 = CR/T1
SA
SC
SD
SF
Total = 4
Therefore, option C is correct

Alternate Solution :
The output of query T1 will be the courses enrolled by student SA i.e CA, CB, CC
The output of query T2 will be the names of the students who enroll all the courses that are the output of query T1 (division operator) i.e CA, CB, CC
From the table we can see that SA, SC, SD, SF have enrolled all the courses so the output of T2 will have 4 row

Forgot your password?

I agree with the Terms.