SELECT T2.allergytype ,  count(*) FROM Has_allergy AS T1 JOIN Allergy_type AS T2 ON T1.allergy  =  T2.allergy GROUP BY T2.allergytype
Show all allergy type with number of students affected.
SELECT T2.allergytype , count ( * ) FROM Has_allergy AS T1 JOIN Allergy_type AS T2 ON T1.allergy = T2.allergy GROUP BY T2.allergytype
select t2 . allergytype , count ( * ) from has_allergy as t1 join allergy_type as t2 on t1 . allergy = t2 . allergy group by t2 . allergytype
Show all allergy type with number of students affected .