MovieExec(name, address, cert, netWorth)
Studio(name, address, presC)
SQL:
Select M.Name
from MovieExec M, Studio S
Where M.Cert=S.PresC
And M.NetWorth >=1000000;
Now, This query will give the name of all the executives which are president of some Studio, and the essential requirement
of an executive to be a president of a studio is that his/her networth >=1000000.
Now, coming to options:
(P) is INCORRECT, as It will select those records, where the networth > 1000000, hence, it can be eliminated, as we're looking for presidents with networth >=1000000. And, result given by P will be subset of our required result.
(Q) is CORRECT, because in the Studio, there will be the records of those people only whose networth>=100000, and if we join Studio with MovieExec with the people with networth <100000, the result set will be empty, because there is no executive who is president of a studio and has networth <1000000.
(R) is also CORRECT, because netoworth>=1000000 is an essential requirement to be a president of studio, but everyone who has networth>=100,000 doesn't need to be a president, Hence the relation Studio will be a subset of MovieExec with executives with networth>1000000.
(S) is INCORRECT, because we can't establish a relation between the Relation Studio and the people with networth<=1000000, because the executives with <=100000 can be more than/less than/equal to the executive with networth >=100000.
Hence, the correct option is (C).