ISRO | ISRO CS 2017 – May | Question 7

What is the output of the following SQL query?

select count(*) from ((select Employee, Department from Overtime_allowance) as S
natural join (select Department, OT_allowance from Overtime_allowance) as T);

(A) 16
(B) 4
(C) 8
(D) None of the above
(E) none


Answer: (B)

Explanation: (select Employee, Department from Overtime_allowance) as S
natural join (select Department, OT_allowance from Overtime_allowance) as T)

Table S                          Table R
Employee     Department          Department     OT_allowance
Rama         Mechanical          Mechanical     5000
Gopi         Electrical          Electrical     2000
Sindhu       Computer            Computer       4000
Mahesh       Civil               Civil          1500

Now when we apply a natural join on S and R, it matches the common attribute Department in both the tables and outputs the common tuples. So, 4 tuples will be given as the output.
Correct option (B)

Quiz of this Question