Let R(a,b) be a schema and Q1 and Q2 are queries on R.
Q1: SELECT * FROM R;
Q2: (SELECT * FROM R) INTERSECT (SELECT * FROM R);
Which of the following statements is true?
(A) Q1 and Q2 produce the same answer.
(B) The answer to Q1 is always contained in the answer to Q2.
(C) The answer to Q2 is always contained in the answer to Q1.
(D) Q1 and Q2 produce different answers.
ans = C given
please explain the logic behind