SQL Server中全半角转换函数

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CREATE   FUNCTION   F_Convert_CharSet(
@string  nvarchar(4000)   -- 输入的字符串
,@flag  tinyint    -- 转换标识(1:全角转半角；其他：半角转全角)
)
      RETURNS   nvarchar(2000)
      WITH   ENCRYPTION
AS
BEGIN
    DECLARE   @i                   int
                  ,@ret               nvarchar(2000)

    select   @i=1
    SET   @ret= ' '
    if(@flag=1)
    begin
  while     SUBSTRING(@string,@i,1) <> ' '
  begin
   if   UNICODE(SUBSTRING(@string,@i,1))> 255
   SET     @ret=@ret+NCHAR(UNICODE(SUBSTRING(@string,@i,1))-
           CASE
            WHEN     SUBSTRING(@string,@i,1)= '。 '     THEN     12244     ELSE         65248
           END     )
  else
   SET     @ret=@ret+(SUBSTRING(@string,@i,1))
   SET     @i=@i+1
  end
    end
    else
    begin
  while   @i <=len(@string)
  begin
   if   unicode(SUBSTRING(@string,   @i,   1)) <256
    select   @ret   =   @ret   +   NCHAR(unicode(SUBSTRING(@string,   @i,   1))+   0xFEE0   )
   else
    select   @ret   =   @ret   +   SUBSTRING(@string,   @i,   1)
   SET   @i=@i+1
  end
    end

return @ret
end