Postgresql计算记录之间的最小时间差

我正在尝试创建一个产生时间差的函数。我首先要选择一个唯一的用户,然后为这个用户选择所有的记录,然后计算这些点和下一个点之间的时间差。它是按升序排列的,然后应该在一张桌子上结束

id, user, time_read, timediff
0, test, 2019-10-12 21:15:02.000000, 0 
1, test, 2019-10-12 21:15:06.000000, 4 seconds
2, test, 2019-10-12 21:15:19.000000, 13 seconds
3, test, 2019-10-12 21:15:23.000000, 4 seconds
etcetera


CREATE TABLE newtable AS
    SELECT null::integer as id, null::character varying as aid,
           null::timestamp, null::interval as timediff;

do $$
declare
   i character varying;
   r mytable;
   e timestamp;
   counter integer := 0;
begin
    for i in
        select distinct(aid) from mytable
    loop
        for r in
            select time_read from mytable
            where aid = i order by time_read asc
        loop
            for e in r
                insert into newtable
                counter, 
                    select aid, e,
                        e-sv.time_read::timestamp
                    from mytable as sv
                    where aid = i and e <> sv.time_read 
                    order by e-sv.time_read::timestamp
                    limit 1;
                counter += 1;
        end loop;
    end loop;
    raise notice '%', i||tripcount::character varying;
end; $$