--主表（类型）结构
Create table #tb_type
(
 id int identity(1,1),
 name nvarchar(50)--名称
)
--子表（记录表）结构
Create table #tb_record
(
 id int identity(1,1),
 typeid int--外键
)

--测试数据
insert into #tb_type values(N'类别1')
insert into #tb_type values(N'类别2')
insert into #tb_type values(N'类别3')
insert into #tb_record values(1)
insert into #tb_record values(1)
insert into #tb_record values(1)
insert into #tb_record values(2)
insert into #tb_record values(2)

go
SELECT 
    a.name,STR(count(b.ID)*100.0/c.con,2,0)+'%'
FROM #tb_type AS a
    LEFT JOIN #tb_record AS b ON a.ID=b.typeid
    CROSS JOIN (SELECT COUNT(*) AS con FROM #tb_record) AS c 
GROUP BY a.name,c.con

------解决方案--------------------
SQL code
select
  a.name as 类别名称,
  isnull(ltrim(cast(count(b.typeid)*100.0/(select count(1) from #tb_record) as dec(18,0))+'%','0%')
from
  #tb_type a,#tb_record b
where
   a.id=b.typeid
group by
   a.name

------解决方案--------------------
SQL code
SELECT 
    a.name AS 类别名称,STR(count(b.ID)*100.0/c.con,2,0)+'%' AS 百分比
FROM #tb_type AS a
    LEFT JOIN #tb_record AS b ON a.ID=b.typeid
    CROSS JOIN (SELECT COUNT(*) AS con FROM #tb_record) AS c 
GROUP BY a.name,c.con

/*
类别名称    百分比
类别1    60%
类别2    40%
类别3     0%
*/

------解决方案--------------------
SQL code
select
  a.name as 类别名称,
  isnull(ltrim(cast(count(b.typeid)*100.0/(select count(1) from #tb_record) as dec(18,0))+'%','0%')
from
  #tb_type a left join #tb_record b
on
   a.id=b.typeid
group by
   a.name