What is the ratio of male and female users in 27-28 age group?
ratio = DIVIDE(COUNT(device_id WHERE gender = 'M' AND `group` = 'M27-28'), COUNT(device_id WHERE gender = 'F' AND `group` = 'F27-28')); 27-28 age group refers to `group` = 'F27-28';
SELECT SUM(IIF(gender = 'M' AND `group` = 'M27-28', 1, 0)) / SUM(IIF(gender = 'F' AND `group` = 'F27-28', 1, 0)) AS r FROM gender_age