求叫一个简单的存储

Question

create proc Statistic
@companyname nvarchar(100),
@total_company int=0 output
as
declare 
@countcompany nvarchar(10)set @countcompany='select @a1=count(1) from company where    companyname='+@companyname    
 exec sp_executesql @countcompany ,N'@a1 int output',@total_company output
大家看看有什么问题,
执行后结果总为0

Answer 1

create proc Statistic
@companyname nvarchar(100),
@total_company int=0 output
as
begin
    declare @countcompany nvarchar(10)    set @countcompany=N'select @a1=count(1) from company where companyname=''' + @companyname + ''''    exec sp_executesql @countcompany ,N'@a1 int output',@total_company output
end
go

Answer 2

--trycreate proc Statistic
@companyname nvarchar(100),
@total_company int output
as
select @total_company=count(1) from company 
where companyname=@companyname
return
go

Answer 3

--调用
declare @total_company int
exec Statistic '公司名', @total_company output
select @total_company