How many females use ZUK Z1 phones in the age group under 23?
females refers to gender = 'F'; ZUK Z1 refers to phone_brand = 'ZUK' AND device_model = 'Z1'; under 23 refers to `group` = 'F23-' ;
SELECT COUNT(T1.device_id) FROM gender_age AS T1 INNER JOIN phone_brand_device_model2 AS T2 ON T1.device_id = T2.device_id WHERE T1.gender = 'F' AND T2.device_model = 'Z1' AND T1.`group` = 'F23-' AND T2.phone_brand = 'ZUK'