SPEED, MySQL - rextester

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create table if not exists ss(ID int, SPEED decimal(9,1), TIME1 datetime);
insert into ss values
(1, 2.5, '2017-01-27 08:23:03'),
(2, 1.9, '2017-01-27 08:22:02'),
(3, 2.0, '2017-01-27 08:21:02'),
(4, 2.1, '2017-01-27 08:20:01'),
(5, 2.3, '2017-01-27 08:19:03');

select * from ss;

select ID, SPEED, t1, t2, TIME_TO_SEC(TIMEDIFF(t2, t1)) T_DIF, 
       (TIME_TO_SEC(TIMEDIFF(t2, t1)) * SPEED) AS DIST
from (
        select ID, SPEED, @t1 as t2, @t1 := TIME1 as t1
        from
            (select @t1 := MAX(TIME1) from ss) x,
            (select ID, SPEED, TIME1 from ss order by TIME1 desc) y
     ) z
;
    
select TIME_TO_SEC(TIMEDIFF(MAX(t2), MIN(t1))) DIF_T, 
       SUM((TIME_TO_SEC(TIMEDIFF(t2, t1)) * SPEED)) TOTAL_DIST,
       (SUM((TIME_TO_SEC(TIMEDIFF(t2, t1)) * SPEED)) / TIME_TO_SEC(TIMEDIFF(MAX(t2), MIN(t1)))) AVG_SPEED
from (
        select ID, SPEED, @t1 as t2, @t1 := TIME1 as t1
        from
            (select @t1 := MAX(TIME1) from ss) x,
            (select ID, SPEED, TIME1 from ss order by TIME1 desc) y
     ) z
;

drop table ss;


absolute service time: 0,38 sec