update ProStatus
set errorcount = p.errorcount
from (select count(ProPK), Prjguid from proofread 
    where status=1 group by prjguid)p
where t.Prjguid = ProStatus.PrjGUID

------解决方案--------------------
上面一个p写成了t
SQL code

 
update ProStatus
set errorcount = p.errorcount
from (select count(ProPK), Prjguid from proofread 
    where status=1 group by prjguid)p
where p.Prjguid = ProStatus.PrjGUID

------解决方案--------------------
update PrjGUID  
set errorcount=b.errorcount
from  PrjGUID a,(select count(ProPK) errorcount, Prjguid from proofread where status=1 group by prjguid
) b
where a.PrjGUID =b.PrjGUID

------解决方案--------------------
update ProStatus
set errorcount = p.errorcount
from (select count(ProPK) errorcount, Prjguid from proofread  
   where status=1 group by prjguid)p
where p.Prjguid = ProStatus.PrjGUID

------解决方案--------------------
SQL code

update a
set a.errorcount=isnull(b.errorcount,0)
from ProStatus a
left join
(select Prjguid,count(ProPK) errorcount
 from proofread where status=1 
 group by prjguid
) b on a.PrjGUID=b.Prjguid

------解决方案--------------------
终于发现问题的根源了，是
p.Prjguid = a.PrjGUID，这句

因为
select Prjguid,count(ProPK) errorcount
  from proofread where status=1  
  group by prjguid

里的status=1 ,导致，如果在proofread 表里没有记录，就不会有结果，并不是count(ProPK)为null，而是根本就不会有该工程的错误数查出来。

而外面又用了a.PrjGUID =b.PrjGUID，错误数不等的，根本一条也查不出来，查出来的都是相等的。