SELECT
SchoolA.student_name AS member_A,
SchoolB.student_name AS member_B,
SchoolC.student_name AS member_C
FROM SchoolA, SchoolB, SchoolC
WHERE
SchoolA.student_id != SchoolB.student_id
AND SchoolA.student_id != SchoolC.student_id
AND SchoolB.student_id != SchoolC.student_id
AND SchoolA.student_name != SchoolB.student_name
AND SchoolA.student_name != SchoolC.student_name
AND SchoolB.student_name != SchoolC.student_name;