`请问一个SQL的写法`很急

``请教一个SQL的写法``很急```
```````我用的是一个人员信息表``
            现在存在这个SQL```````
select   count(distinct   R.emp_id)   from   report_address   as   R,employee   as   E   where   E.emp_id=R.emp_id     group   by   sign_date
              我想对所求列进行磊加``
    应该怎么写语句啊``

------解决方案--------------------
這個意思？

Select SUM(countemp_id) From (select count(distinct R.emp_id) As countemp_id from report_address as R,employee as E where E.emp_id=R.emp_id group by sign_date) A