CREATE FUNCTION F_strcompare(@str1 VARCHAR(8000),
                             @str2 VARCHAR(8000))
RETURNS VARCHAR(10)
AS
  BEGIN
      DECLARE @i   INT,
              @j   INT,
              @k   INT,
              @ret VARCHAR(10)

      SELECT @i = MAX(strlen),
             @j = MIN(strlen),
             @k = 0
      FROM   (SELECT strlen=Len(@str1)
              UNION
              SELECT strlen=Len(@str2)) t

      IF( @j = 0 )
        RETURN '0%'

      WHILE @j > 0
        BEGIN
            IF Substring(@str1, @j, 1) = Substring(@str2, @j, 1)
              SET @k=@k + 1

            SET @j=@j - 1
        END

      SET @ret = Rtrim(CAST(@k * 100.0 / @i AS NUMERIC(3, 0))) + '%'

      RETURN @ret
  END

GO

SELECT dbo.F_strcompare('中国人','中华人民共和国')