Relation R(x,y) currently consists of only one tuple (NULL, NULL). Which of the following queries will produce a nonempty output? That is, at least one tuple will be produced, although the tuple(s) may have NULL's.
a. SELECT * FROM R WHERE x IS NULL
b. SELECT * FROM R WHERE x = NULL
c. SELECT * FROM R WHERE x = y
d. SELECT * FROM R WHERE x <> 10
Answer: A