SELECT SUM(DISTINCT NVL(subject1,0)), MAX(subject1) FROM marks WHERE subject1 > subject2;
SELECT student_name subject1 FROM marks WHERE subject1 > AVG(subject1);
SELECT SUM(subject1+subject2+subject3) FROM marks WHERE student_name IS NULL;
SELECT student_name,SUM(subject1) FROM marks WHERE student_name LIKE ‘R%’;
