Find the ratio / mix of students by gender in each class

 3)Find the ratio / mix of students by gender in each class 

There is a table students - 
Columns are - name , class , dob , gender , marks 

SELECT class,
    COUNT(IF(gender = 'male', 1, NULL)) count_male,
    COUNT(IF(gender = 'female', 1, NULL)) count_female,
    COUNT(IF(gender = 'male', 1, NULL))/COUNT(IF(gender = 'female', 1, NULL)) as ratio
FROM
    students

group by class ;