从mysql迁移到GBase 8s数据库时，原有timestampdiff()函数在GBase 8s中不可用，因此需要自己创建相应的函数，可以使用C或者JAVA创建自定义例程，也可以使用存储过程。以下以存储过程方式创建。
该函数的功能是：按第一个参数interval的值，获取dt1与dt2的日期时间差值。如果dt1 > dt2且isabs为'f'时, 将显示负值。

-- timestampdiff(interval,dt1,dt2[,isabs]);
-- interval取值为：year,quarter,month,week,day,hour,minute,second
-- 如果dt1 > dt2且isabs为'f'时, 将显示负值
-- 修改于2023-08-25
drop function if exists timestampdiff;
create function timestampdiff(itv varchar(10), dt1 datetime year to fraction(5), dt2 datetime year to fraction(5), isabs boolean default 't')
returning bigint with (not variant);
  define v_value bigint;
  define v_1lt2 boolean;
  define v_interval varchar(30);
  define v_itv varchar(10);
  on exception
    return null;
  end exception;
 
  let v_value = 0;
  let v_itv = lower(itv);
  let v_1lt2 = 'f';
   
  if dt1 > dt2 then
    let v_interval = dt1 - dt2;
    let v_1lt2 = 't';
  else
    let v_interval = dt2 - dt1;
  end if;
  if v_itv = 'day' then
    let v_value = substr(v_interval,1,9)::bigint;
  elif v_itv = 'hour' then
    let v_value = substr(v_interval,1,9)::bigint * 24 + substr(v_interval,11,2)::bigint;
  elif v_itv = 'minute' then
    let v_value = (substr(v_interval,1,9)::bigint * 24 + substr(v_interval,11,2)::bigint) * 60 + substr(v_interval,14,2);
  elif v_itv = 'second' then
    let v_value = ((substr(v_interval,1,9)::bigint * 24 + substr(v_interval,11,2)::bigint) * 60 + substr(v_interval,14,2)) * 60 + substr(v_interval,17,2);
  elif v_itv = 'week' then
    let v_value = substr(v_interval,1,9)::bigint / 7;
  elif v_itv = 'month' then
    let v_value = MONTHS_BETWEEN(dt1,dt2)::bigint;
  elif v_itv = 'quarter' then
    let v_value = MONTHS_BETWEEN(dt1,dt2)::bigint / 3;
  elif v_itv = 'year' then
    let v_value = MONTHS_BETWEEN(dt1,dt2)::bigint / 12;
  end if;
 
  if v_1lt2 = 't' and isabs = 'f' then
    return 0 - v_value;
  else
    return v_value;
  end if;
end function;

示例：

-- 两个日期差值，day
select timestampdiff('DAY', DATE('2020-05-14'), DATE('2020-05-31')) from dual;

结果: 17

-- 两个日期时间差值，second
select timestampdiff('second', to_date('2020-05-14 00:00:00','yyyy-mm-dd hh24:mi:ss'), DATETIME(2020-05-01 00:00:00) YEAR to SECOND,'f') from dual;

结果：-1123200