SQL server 计算年龄明细问题

/*计算明细年龄问题*/

DECLARE @ADATE DATETIME, @BIRTHDAY DATETIME
 , @AYEAR INT,@AMONTH INT,@ADAY INT,@BDAY INT, @RVALUE VARCHAR(20)
SET @RVALUE = ''
SET @BIRTHDAY ='2019-06-21 10:00:00.000'
SET @ADATE = GETDATE()  
SET @ADAY = DATEDIFF(DAY, @BIRTHDAY, @ADATE) --当前日期与生日的日期

      IF @ADAY >   --即 出生日期大于当前日期，生日day>当前day
      BEGIN
        --当前日期与生日的月份差值
        SELECT @AMONTH = DATEDIFF(MONTH, @BIRTHDAY, @ADATE),
        --DATEPART 用于返回日期的单独部分，当前日期的日减去生日的日，赋值给@BDAY
         @BDAY = DATEPART(DAY, @ADATE) - DATEPART(DAY, @BIRTHDAY)
        
        SET @AYEAR = @AMONTH / 12  --年=总月份/12
        SET @AMONTH = @AMONTH % 12 --总月份除以12取余
   --如果当前日减去生日的日小于0 ，将总月份除以12的余数减一
        IF @BDAY <  SET @AMONTH = @AMONTH - 1 
        
   --如果上一个条件成立，且当@AMONTH=0 时，@AMONTH = @AMONTH - 1<0 ，条件成立，年龄=@AYEAR-1，月份=@AMONTH=12+@AMONTH
        IF @AMONTH <  SELECT @AYEAR = @AYEAR - 1, @AMONTH = 12 + @AMONTH 
      
        IF @BDAY < 
        BEGIN
          SET @BIRTHDAY = DATEADD(MONTH, @AMONTH, @BIRTHDAY)
        
          SET @BIRTHDAY = DATEADD(YEAR, @AYEAR, @BIRTHDAY)
          
          SET @BDAY = DATEDIFF(DAY, @BIRTHDAY, @ADATE)
          
        END
      SET @RVALUE=CAST(@AYEAR AS VARCHAR)+'岁'+CAST(@AMONTH  AS VARCHAR)+'月'+CAST(@BDAY  AS VARCHAR)+'日'
      SELECT @RVALUE

     END