mysql order by和union的联合使用

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今天在做一个统计报表的时候用到了order by desc排序，结果发现它不能和 union一起使用
Error Code : 1054
Unknown column 't2.count_vod' in 'order clause'
 
原句：
select 'a week upload',count(*)
from update_table
where  date_format(time,'%Y%m%d') = date_format(DATE_ADD(now(),INTERVAL -7 DAY),'%Y%m%d')
union
select 'a week upload title',t1.title,t2.user_count
from update_table as t1 ,update_user as t2
where where  date_format(time,'%Y%m%d') = date_format(DATE_ADD(now(),INTERVAL -7 DAY),'%Y%m%d') and t1.user_count=t2.user_count
order by  t1.user_count desc;
 
利用临时表来解决这个问题：
select 'a week upload',count(*)
from update_table
where  date_format(time,'%Y%m%d') = date_format(DATE_ADD(now(),INTERVAL -7 DAY),'%Y%m%d')
union
select * from (select 'a week upload title',t1.title,t2.user_count
from update_table as t1 ,update_user as t2
where where  date_format(time,'%Y%m%d') = date_format(DATE_ADD(now(),INTERVAL -7 DAY),'%Y%m%d') and t1.user_count=t2.user_count
order by  t1.user_count desc) as temp;
 
如果有多个查询结果需要放在一起可以用类似的方式解决