Question

Given three relational schemas R(AB), S(A), and T(B), and let r(R), s(S), and t(T) be the relations (relation table or relation instance) corresponding to R, S, and T respectively as the following:
AB                      A      B
______       ___    ___
a1 b1 a1 b2
a2 b1       a3            b4
a3 b1
a1 b2
a2 b2
a3 b2
a1 b4
a2 b4
r(R)             s(S)    t(T)

1. Please give the result of table R divideby table S.
2. Please give the result of table R divideby table T.
3. Can table S be divided by table T?
4. Can table T be divided by table S?

Answer 1

1. your table elements are not very clear . but still , the answer would be for r divide by s.means all B entries of R where A column matches for both R and S.

2. Similary here also ,all A entries of R where B column matches for both R and T.

3 no , Since no common columns are there to divide.

4. Again for the same reason as above it is not possible