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)
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