sql 2005 数据查询统计大数计算精确度不准确 不知道什么原因 有点费解

if object_id('tb') is not null 

drop table tb 



create table tb(type varchar(20),accessoryNo varchar(20),deviceNo varchar(10),lastTime int) 

insert tb 

select 'A','s10','z11',10 union all 

select 'B','s10','z11',11 union all 

select 'C','s11','z12',5 union all 

select 'A','s10','z11',9 union all 

select 'A','s10','z13',9 union all 

select 'B','s10','z11',3 



if object_id('fees') is not null 

drop table fees



create table fees(id int,fee numeric(18, 3))

insert fees 

select 1, 75188.580 

go 



declare @sql1 nvarchar(4000) 

declare @count int

declare @sql nvarchar(4000) 



set @sql1=N'select @a=sum(lastTime)  from tb'

exec sp_executesql @sql1,N'@a int output',@count output

set @sql='select row_number() over(order by [type]) as [序号],[type] as [型号],accessoryNo as [零件号],sum(lastTime) as [持续时间],1.0*sum(lastTime)/'+cast(@count as varchar(20))+'*fee as [分配额

]'

set @sql=@sql+' from tb,fees where id = 1 group by type,accessoryNO,fee' 

set @sql=@sql+' union all select '''' as 序号,''全部型别'' as [型号] ,''全部零件'' as [零件号],sum(lastTime)  as [持续时间],1.0*sum(lastTime)/'+cast(@count as varchar(20))+'*fee as [分配额] from tb,fees group by fee'

exec(@sql) 



drop table tb 

drop table fees



--查询结果是



/*



(1 行受影响)

序号         型号        零件号        持续时间        分配额

-------------------- -------------------- -------------------- ----------- ---------------------------------------

1           A             s10           28          44793.145403520    即75188.58/47*28=44793.196596

2           B             s10           14          22396.572701760    即75188.58/47*14=22396.598297872

3           C             s11           5           7998.711517560     即75188.58/47*5=7998.785106383

0       全部型别        全部零件        47          75188.580000000



(4 行受影响)



即后面是我用计算器计算的



*/