Let R and S be relational schemas such that R = {a, b, c} and S = {c}. Now consider the following queries on the database:1. R - S - R - S ( R - S(r) S - r - S , S (r))2. { t | t R - S(r) u s ( v r ( u = v[s] t = v[ R - S ] ) ) }3. { t | t R - S(r) u s ( u s ( u = v[s] t = v[ R - S ] ) ) }4. Select R.a, R. b From R, S Where R.c = S.c Which of the above queries are equivalent?

Let R and S be relational schemas such that R = {a, b, c} and S = {c}.

1.	Let R and S be relational schemas such that R = {a, b, c} and S = {c}. Now consider the following queries on the database: 1. _{R - S} - _{R - S} ( _{R - S}(r) S - _{r - S , S} (r)) 2. { t \| t _{R - S}(r) u s ( v r ( u = v[s] t = v[ R - S ] ) ) } 3. { t \| t _{R - S}(r) u s ( u s ( u = v[s] t = v[ R - S ] ) ) } 4. Select R.a, R. b From R, S Where R.c = S.c Which of the above queries are equivalent?
A.	1 and 2
B.	1 and 3
C.	2 and 4
D.	3 and 4
Answer» D. 3 and 4

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