【叶子函数分享五十七】计算个人所得税函数 有段代码看不懂，求讲解
create function TaxRateOfPersonal
(
  @fvalue numeric(18,4)
)
returns numeric(18,4)
as
begin
  declare @i numeric(18,4)
  declare @basetable table(id int,
  basemoney numeric(18,4),minvalue numeric(18,4),
  maxvalue numeric(18,4),taxs numeric(18,4))
   
  insert into @basetable
  select 1,2000,0,1000,0.05 union all
  select 2,2000,1000,3000,0.1 union all
  select 3,2000,3000,6000,0.15 union all
  select 4,2000,6000,10000,0.2 union all
  select 5,2000,10000,15000,0.25
  select @i=sum(case when @fvalue>basemoney+maxvalue
then maxvalue-minvalue else @fvalue-basemoney-minvalue end *taxs)
from @basetable where basemoney+minvalue<=@fvalue
  return @i
end
红色部分 


------解决方案--------------------
sum(当什么情况满足了（也就是when后面的），然后怎么算（then后面的），不满足（else后面的），
又怎么算，有什么不懂得？)--sum我就不解释了吧，求和