Consider two tables in a relational database with columns and rows as follows:

 Table: Student

Roll_no	Name	Dept_id
1	ABC	1
2	DEF	1
3	GHI	2
4	JKL	3

 Table: Department

Dept_id	Dept_name
1	A
2	B
3	C

Roll_no is the primary key of the Student table, Dept_id is the primary key of the Department table and Studetn.Dept_id is a foreign key from
Department. Dept_id.

What will happen if we try to execute the following two SQL statements?

(i) update Student set Dept_id = Null where Roll_no =1
(ii) update Department set Dept_id = Null where Dept_id =1

Consider the set of relations shown below and the SQL query that follows.

Students: (Roll_number, Name, Date_of_birth)
Courses: (Course number, Course_name, Instructor)
Grades: (Roll_number, Course_number, Grade)

Select distinct Name
From Students, Courses, Grades
Where Students.Roll_number = Grades.Roll_number
      and Courses.Instructor = 'Korth'
      and Courses.Course_number = Grades.Course_number
      and Grades.grade = 'A';

Which of the following sets is computed by the above query?

In SQL, relations can contain null values, and comparisons with null values are treated as unknown. Suppose all comparisons with a null value are treated as false. Which of the following pairs is not equivalent?

Given relations r( w, x ) and s( y, z ), the result of

select distinct w,x
from r, s;

is guaranteed to be same as r, provided