SELECT *
FROM Student_1 S1
WHERE NOT EXISTS
  (SELECT *
  FROM Student_2 S2
  WHERE S1.name = S2.name
  AND S1.age    = S2.age
  AND S1.score  = S2.score
  )
UNION ALL
SELECT *
FROM STUDENT_2 S2
WHERE NOT EXISTS
  (SELECT *
  FROM STUDENT_1 S1
  WHERE S1.name = S2.name
  AND S1.age    = S2.age
  AND S1.score  = S2.score
  );

(SELECT * FROM Student_1
MINUS
SELECT * FROM Student_2)
UNION ALL
(SELECT * FROM Student_2
MINUS
SELECT * FROM Student_1)

SELECT DISTINCT name, age, score FROM (
SELECT * FROM Student_1
UNION ALL
SELECT * FROM Student_2
)GROUP BY name, age, score HAVING COUNT(*)=1 ;