(select `id` from table where uid = 2 order by createtime desc limit 3) UNION ALL 

(select `id` from table where uid = 3 order by createtime desc limit 3) UNION ALL 

(select `id` from table where uid = 7 order by createtime desc limit 3) UNION ALL 

(select `id` from table where uid = 11 order by createtime desc limit 3) UNION ALL 

(select `id` from table where uid = 14 order by createtime desc limit 3) UNION ALL 

(select `id` from table where uid = 24 order by createtime desc limit 3)