Below is the list of tables from the database along with their columns and datatype. Need to generate an accurate SQL query for the question.
Only use the columns present in the respective table. Only use the columns which are required to generate the SQL query. Only use table joins if required and not otherwise.

### Tables ###
TABLE: CREATE TABLE Allergy_Type ( Allergy VARCHAR(20), AllergyType VARCHAR(20) )
TABLE: CREATE TABLE Has_Allergy ( StuID INTEGER, Allergy VARCHAR(20) )
TABLE: CREATE TABLE Student ( StuID INTEGER, LName VARCHAR(12), Fname VARCHAR(12), Age INTEGER, Sex VARCHAR(1), Major INTEGER, Advisor INTEGER, city_code VARCHAR(3) )

### Question ###
How many students are affected by each allergy type Visualize by bar chart, could you display total number in descending order please?

### Accurate SQL ###

SELECT AllergyType, COUNT(*) FROM Has_Allergy AS T1 JOIN Allergy_Type AS T2 ON T1.Allergy = T2.Allergy GROUP BY T2.AllergyType ORDER BY COUNT(*) DESC