Question: What percentage of vivo devices belong to users with no information?
SQL: 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'