gate ,Plz explan by using tables

Question

A relational database contains two tables student and department in which student table has columns (roll_no, name and dept_id )and department table has columns (dept-id and dept-name). The following insert statements were executed successfully to populate the empty tables:

Insert into department values (1, 'Mathematics');
Insert into department values(1, 'Physics');
Insert into department values(1, 'Navin', 1);
Insert into student values (2, 'Ravi', 2);
Insert into student values (3, `Gitu', 1);

How many rows and columns will be retrived by the following SQL, statement?

Select * from student, department;

A.	0 row and 4 columns **
B.	3 rows and 4 columns
C.	3 rows and 5 columns
D.	6 rows and 5 columns

Answer 1

Answer should be (B) 3 rows, 4 coumns

Rollno	Name	Dept id	Dept Name
1	Navin	1	Math
2	Ravi	2	Physics
3	Gitu	1	math

Comments

No its answer is 6 rows and 5 columns.It is gate previous year question and solved too but expalanation was not clear to me.

Answer 2

Depratment table(D):

---------------------------

1   Mathematics

1   Physics

 

student table(S):

------------------------------------

1 Navin 1

2 Ravi   2

3 Gitu   1

 

Now, we are taking the cross product of 2 tables: So, result contains following columns:

S.roll_no      S.name     S.dept_id    D.dept_id     D.dept_name

----------------------------------------------------------------------------------------------------------------

Combine the columns only when its join operation because join operation is considered as set operation on column names.

So, (D) is correct answer.