Q2.24MCQ2 marks, −0.5Which of the following relational calculus expression is not safe?(A){t∣∃u∈R1(t[A]=u[A])∧¬∃s∈R2(t[A]=s[A])}\left\{t \mid \exists u \in R_1\left(t[A] = u[A]\right) \land \neg \exists s \in R_2 \left(t[A] = s[A]\right)\right\}{t∣∃u∈R1(t[A]=u[A])∧¬∃s∈R2(t[A]=s[A])}(B){t∣∀u∈R1(u[A]="x"⇒∃s∈R2(t[A]=s[A]∧s[A]=u[A]))}\left\{ t \mid \forall u \in R_1\left(u[A]="x" \Rightarrow \exists s \in R_2\left(t[A] = s[A] \land s[A] = u[A]\right)\right) \right\} {t∣∀u∈R1(u[A]="x"⇒∃s∈R2(t[A]=s[A]∧s[A]=u[A]))}(C){t∣¬(t∈R1)}\left\{t \mid \neg (t \in R_1)\right\} {t∣¬(t∈R1)}(D){t∣∃u∈R1(t[A]=u[A])∧∃s∈R2(t[A]=s[A])}\left\{t \mid \exists u \in R_1\left(t[A]=u[A]\right) \land \exists s \in R_2 \left(t[A] = s[A]\right)\right\}{t∣∃u∈R1(t[A]=u[A])∧∃s∈R2(t[A]=s[A])}Sign in to save attempts.Show answer← PreviousNext →SolutionsDiscussionLoading…Sign in with Google