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
[{'AllergyType': 'animal', 'count(*)': 8}, {'AllergyType': 'environmental', 'count(*)': 23}, {'AllergyType': 'food', 'count(*)': 28}]