What is the difference between the number of molecules that are carcinogenic and those that are not?
label = '+' means molecules are carcinogenic; label = '-' means molecules are non-carcinogenic; difference = SUBTRACT(SUM(label = '+'), SUM(label = '-'))
SELECT COUNT(CASE WHEN T.label = '+' THEN T.molecule_id ELSE NULL END) - COUNT(CASE WHEN T.label = '-' THEN T.molecule_id ELSE NULL END) AS diff_car_notcar FROM molecule t