sqlserver取汉字的首字母

Create  function fun_getPY
 (
    @str nvarchar(4000)
 )
returns nvarchar(4000)
as
begin

  declare @word nchar(1),@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'腂'
                     union all select 'H',N'夻'
                     union all select 'J',N'攈'
                     union all select 'K',N'穒'
                     union all select 'L',N'鱳'
                     union all select 'M',N'旀'
                     union all select 'N',N'桛'
                     union all select 'O',N'漚'
                     union all select 'P',N'曝'
                     union all select 'Q',N'囕'
                     union all select 'R',N'鶸'
                     union all select 'S',N'蜶'
                     union all select 'T',N'籜'
                     union all select 'W',N'鶩'
                     union all select 'X',N'鑂'
                     union all select 'Y',N'韻'
                     union all select 'Z',N'咗'
                      ) T
                   where word>=@word collate Chinese_PRC_CS_AS_KS_WS
                   order by PY ASC
                          )
                      else @word
                 end)
    set @str=right(@str,len(@str)-1)
  end

  return @PY

end