NIELIT 2016 MAR Scientist B - Section C: 42

Question

The relational algebra expression equivalent to the tuple calculus expression

$\{t\mid t ​ \in ​ r \land (t[A]=10 \land t[B]=20)\}$ is

• A. $\sigma_{(A=10\:\lor\:B=20)}(r)$
• B. $\sigma_{(A=10)}(r)\cup\sigma_{(B=20)}(r)$
• C. $\sigma_{(A=10)}(r)\cap\sigma_{(B=20)}(r)$
• D. $\sigma_{(A=10)}(r)-\sigma_{(B=20)}(r)$

Answer 1

Option C

t ia table have two attribute A,B

$({t∣t​∈​r∧(t[A]=10∧t[B]=20)}$ MEANS one of the tuple of table t value of A=10 and B=20

 

t.A	t.B
10	20
30	40

here r is table with attribute A,B

$σ(A=10)(r)∩σ(B=20)(r)$ means one of the tuple of table r value of A=10 and B=20