What percentage of vivo devices belong to users with no information?
percentage = MULTIPLY(DIVIDE(SUM(gender = NULL and age = NULL and `group` = NULL), COUNT(device_id)), 1.0); vivo devices refers to phone_brand = 'vivo'; no information refers to gender = NULL AND age = NULL AND `group` = NULL;
SELECT SUM(IIF(T1.gender IS NULL AND T1.age IS NULL AND T1.`group` IS NULL, 1, 0)) / COUNT(T1.device_id) 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'