请教多表查询结果求和？

SQL code

select a.piaolei,a.renshu,b.mingcheng as pl from Tbl_checkIn a,tbl_PiaoLei bwhere a.piaolei=b.bianhao and convert(char(10),CheckInTime,120) >= '2012-08-16' and convert(char(10),CheckInTime,120) <= '2012-08-16' and CheckInNo='01' and left(e.mingcheng,3)='北京市'

想直接把查询出来的结果根据a.renshu只要求出总和就可以，请问应该怎么写？谢谢！

[解决办法]

SQL code

select sum(a.renshu) as renshufrom Tbl_checkIn a,tbl_PiaoLei bwhere a.piaolei=b.bianhao and convert(char(10),CheckInTime,120) >= '2012-08-16' and convert(char(10),CheckInTime,120) <= '2012-08-16' and CheckInNo='01' and left(e.mingcheng,3)='北京市'
[解决办法]
SQL code
select renshu,count(1) from(select a.piaolei,a.renshu,b.mingcheng as pl from Tbl_checkIn a,tbl_PiaoLei bwhere a.piaolei=b.bianhao and convert(char(10),CheckInTime,120) >= '2012-08-16' and convert(char(10),CheckInTime,120) <= '2012-08-16' and CheckInNo='01' and left(e.mingcheng,3)='北京市')tgroup by  人数