SQL 生日得到年龄

CREATE  FUNCTION ufn_hr_getagefrombirthday
(
    @birthday DATE,
    @now DATE  =NULL  

)
RETURNS VARCHAR(20)
BEGIN  

    IF (@now IS NULL OR @now = '')
    BEGIN
        SET @now = GETDATE();
    END;  

    DECLARE @age INT;
    SET @age = 0;  

    DECLARE @result VARCHAR(20);  

    WHILE (DATEADD(YEAR, @age, @birthday) < @now)
    BEGIN
        SET @age = @age + 1;
    END;  

    SELECT @result
        = CAST(CASE
                   WHEN (@age - 1) < 0 THEN
                       0
                   ELSE
        (@age - 1)
               END AS VARCHAR(4)) + '岁'
          + CAST(DATEDIFF(
                             DAY,
                             DATEADD(   YEAR,
                                        CASE
                                            WHEN (@age - 1) < 0 THEN
                                                0
                                            ELSE
                                        (@age - 1)
                                        END,
                                        DATEADD(DAY, 1, @birthday)
                                    ),
                             DATEADD(YEAR, @age, DATEADD(DAY, 1, @birthday))
                         ) + 1 - (DATEDIFF(DAY, @now, DATEADD(YEAR, @age, DATEADD(DAY, 1, @birthday)))) AS VARCHAR(4))
          + '/'
          + CAST(DATEDIFF(
                             DAY,
                             DATEADD(YEAR, @age - 1, DATEADD(DAY, 1, @birthday)),
                             DATEADD(YEAR, @age, DATEADD(DAY, 1, @birthday))
                         )
AS      VARCHAR(4))  + '';  

    RETURN @result;
END;