select a.id,a.gsmc,count(b.companyId) gsum from company a
left join gongying b on a.id=b.companyId
group by a.id,a.gsmc

------解决方案--------------------

SQL code


Create table #company
(
 id int identity(1,1),
 gsmc nvarchar(50)
)
create table #gongying
(
  id int identity(1,1),
  companyId int
)
insert #company
select 'A' union all
select 'B' union all
select 'C' union all
select 'D' 

insert #gongying
select 2 union all
select 2 union all
select 4 union all
select 1

select a.id,a.gsmc,count(b.companyId) gsum from #company a
left join #gongying b on a.id=b.companyId
group by a.id,a.gsmc

drop table #company,#gongying

--1    A    1
--2    B    2
--3    C    0
--4    D    1