SELECT COUNT(sub.id) AS cnt
FROM (
SELECT CONCAT(m.`building_number`, "-", m.`room_number`) AS id
FROM `rent_detail` m
INNER JOIN `rent_building` b ON b.`user_id` = m.`user_id` AND b.`building_number` = m.`building_number`
LEFT JOIN `rent_town` t ON t.`post_code` = b.`post_code`
LEFT JOIN `rent_line_station` l ON l.`user_id` = m.`user_id` AND l.`building_number` = m.`building_number` AND l.`room_number` = m.`room_number`
GROUP BY
m.`building_number`
, m.`room_number`
) sub
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