Write a query in *********** relational algebra********** for the following requ

Question

Write a query in ***********relational algebra********** for the following requests:

a. Find all airlines that fly to all Canadian airports.

b. Find all airlines that fly to a Canadian airport but not to any US Airport.

c. Find the locations of all airports with at least one flight to New York.

Consider the following relational schema. Flight(number:integer,aie string, from: string, to: string) CanAirport(code: string, location: string) USAirport(code: string, location: string) The "from" and "to" fields in the Flight table point to the "code" fields in the airport table. For example, a typical entry in the Flight table might be 56, AIRC, YEG, YYV and a typical entry in the CanAirport table might be YEG, Edmonton.

Explanation / Answer

a. select airline from Flight where to in(select code from CanAirport);
b. select airline from Flight where to in(select code from CanAirport) AND to not in(select code from USAirport);
c. select location from CanAirport where code in(select from from Flight where to='New York') UNION select location from USAirport where code in(select from from Flight where to='New York')

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