SELECT 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. Visualize by bar chart.
CREATE TABLE Student (
    StuID INTEGER,
    LName VARCHAR(12),
    Fname VARCHAR(12),
    Age INTEGER,
    Sex VARCHAR(1),
    Major INTEGER,
    Advisor INTEGER,
    city_code VARCHAR(3)
)

CREATE TABLE Has_Allergy (
    StuID INTEGER,
    Allergy VARCHAR(20)
)

CREATE TABLE Allergy_Type (
    Allergy VARCHAR(20),
    AllergyType VARCHAR(20)
)