Thank you.

I agree with you. a lot of difficult problem solve by using relational algebra.

Dr. CJ Date offered two methods but I was looking for the best solution for division operator.

here is a method: Please exec following script before exec this query

-- My Method

SELECT DISTINCT pilot

FROM PilotSkills AS PS

WHERE NOT EXISTS (

SELECT plane FROM Hangar

EXCEPT

SELECT plane FROM PilotSkills

WHERE PS.pilot=pilot

)

/*

CREATE TABLE PilotSkills

(pilot CHAR(15) NOT NULL,

plane CHAR(15) NOT NULL,

PRIMARY KEY (pilot, plane));

INSERT INTO PilotSkills

SELECT pilot='Celko', plane='Piper Cub'

UNION

SELECT 'Higgins','B-52 Bomber'

UNION

SELECT 'Higgins','F-14 Fighter'

UNION

SELECT 'Higgins','Piper Cub'

UNION

SELECT 'Jones','B-52 Bomber'

UNION

SELECT 'Jones','F-14 Fighter'

UNION

SELECT 'Smith','B-1 Bomber'

UNION

SELECT 'Smith','B-52 Bomber'

UNION

SELECT 'Smith','F-14 Fighter'

UNION

SELECT 'Wilson','B-1 Bomber'

UNION

SELECT 'Wilson','B-52 Bomber'

UNION

SELECT 'Wilson','F-14 Fighter'

UNION

SELECT 'Wilson','F-17 Fighter'

CREATE TABLE Hangar

(plane CHAR(15) NOT NULL PRIMARY KEY);

INSERT INTO Hangar

SELECT plane='B-1 Bomber'

UNION

SELECT 'B-52 Bomber'

UNION

SELECT 'F-14 Fighter'

*/