Let R = (A, B) and S = (A, C), and let r (R) and s(S) be relations.

Write SQL Queries equivalent to the following domain relational-

calculus expressions:

a. {< a > | $\exists b (< a, b > \epsilon¸r \wedge b$ = 17)}

b. {< a, b, c > | < a, b > $\epsilon¸ r \wedge < a, c > \epsilon¸ $s}

c. {< a > $ | \exists b (< a, b > \epsilon ,r ) \vee \forall c (\exists d (< d, c > \epsilon s) \Rightarrow< a, c > \epsilon ,$ s)}

d. {< a > | $\exists c (< a, c > \epsilon, s \wedge \exists b1, b2 (< a, b1 > \epsilon, r \wedge < c, b2 >

\epsilon r \wedge b1 > b2$))}