What is the ratio of female users to male users who uses a vivo device?
ratio = DIVIDE(SUM(gender = 'M' WHERE phone_brand = 'vivo'), SUM(gender = 'F' WHERE phone_brand = 'vivo')); female refers to gender = 'F'; male refers to gender = 'M'; vivo device refers to phone_brand = 'vivo';
SELECT SUM(IIF(T1.gender = 'M', 1, 0)) / SUM(IIF(T1.gender = 'F', 1, 0)) AS per FROM gender_age AS T1 INNER JOIN phone_brand_device_model2 AS T2 ON T1.device_id = T2.device_id WHERE T2.phone_brand = 'vivo'