MySQL中以逗号分割的字段可以直接快速连表查询

SELECT a.id, GROUP_CONCAT(c.name)
    FROM table1 a
    LEFT JOIN (SELECT aid, GROUP_CONCAT(`cid`) AS cids FROM table2 GROUP BY `aid`) b ON a.id = b.aid
    LEFT JOIN table3 c ON FIND_IN_SET(c.id, b.cids)
    GROUP BY a.id;