汉字转拼音首字母

Create function [dbo].[fun_getPY](@str nvarchar(4000)) 
returns nvarchar(4000) 
as 
begin 
declare @word nchar(1)
declare @PY nvarchar(4000) 
set @PY=''
while len(@str)>0 
begin 
    set @word=left(@str,1)

    --如果非汉字字符，返回原字符 
    set @PY=@PY+(case when unicode(@word) between 19968 and 19968+20901 
then ( 
                            select top 1 PY 
                            from 
                            ( 
                         select 'A' as PY,N'驁' as word 
                     union all select 'B',N'簿' 
                     union all select 'C',N'錯' 
                     union all select 'D',N'鵽' 
                     union all select 'E',N'樲' 
                     union all select 'F',N'鰒' 
                     union all select 'G',N