SELECT 
    c.id challenge_id,
    c.subject challenge_name,
    c.shixun_id,
    c.created_at,
    c.updated_at,
    c.status,
    c.position,
    c.task_pass,
    c.score,
    c.visits,
    c.challenge_tags_count,
    t.challenge_tag
FROM 
    challenges c
LEFT JOIN (
    SELECT 
        challenge_id, 
        GROUP_CONCAT(challenge_tags.`name` SEPARATOR '\t') AS 'challenge_tag'
	FROM challenge_tags 
    GROUP BY challenge_id) t
ON 
    c.id = t.challenge_id