直接利用 distinct

SELECT
    DATE_FORMAT( create_time, '%Y-%m-%d' ) AS days,
    count( * ) count,
       count(distinct user_id)


FROM
    b_user_login_log
WHERE
    DATE_SUB( CURDATE( ), INTERVAL 7 DAY ) <= create_time
GROUP BY
    days;

查询当前设备id

SELECT
    DATE_FORMAT( create_time, '%Y-%m-%d' ) AS days,
    count( * ) count,
    GROUP_CONCAT( user_id ) AS userIds
FROM
    b_user_login_log
WHERE
    DATE_SUB( CURDATE( ), INTERVAL 7 DAY ) <= create_time
GROUP BY
    days;