performance - 计算百分比的更快方法？

Question

我目前使用这种方法得出百分比:

declare @height table
(
    UserId int,
    tall bit
)
insert into @height
select  1, 1 union all
select  2, 1 union all 
select 6, 0 union all
select  3, 0 union all 
select 7, 0 union all
select  4, 1 union all 
select 8, 0 union all
select  5, 0

declare @all decimal(8,5)

select 
    @all = count(distinct UserId)
from @height

select 
    count(distinct UserId) / @all Pct
from @height
where tall = 1  

结果:0.375000000

有没有更好的方法来做到这一点？如您所见，@height

table 被击中了两次。

谢谢!

Answer 1

这允许您只点击一次表格，并为您的给定数据集提供相同的结果。

declare @height table
(
    UserId int,
    tall bit
)
insert into @height
select  1, 1 union all
select  2, 1 union all 
select 6, 0 union all
select  3, 0 union all 
select 7, 0 union all
select  4, 1 union all 
select 8, 0 union all
select  5, 0


select SUM(convert(decimal(8,5), tall)) / convert(decimal(8,5), COUNT(*)) Pct
from @height

根据您的要求，这可能适用于重复的用户 ID。至少它给出的结果与您的结果相同。

select SUM(convert(decimal(8,5), tall)) / convert(decimal(8,5), COUNT(distinct userid)) Pct
from 
    (select distinct UserId, tall
    from @height) t