select c.*,u.user_name as host_name ,uc.user_name as create_name,(select group_concat(case when real_name is null then user_name else real_name end) from user where INSTR(c.invite_user,concat(',',id,','))>0
order by find_in_set(id,c.invite_user)) as invite
from communicate c left join user u on c.host=u.id left join user uc on c.create_user =uc.id
invite_user字段格式為：,1,5,2,3,
group_concat():逗號分隔，將一列數據
find_in_set():按照指定的ID排序