Hallar la diferencia entre el último y el penúltimo término

Modifiqué / simplifiqué la solución de Shadkhan. Funciona para MySQL, Sqlite, PostgreSQL

violín

SELECT e1.event_type, (e1.value - e2.value) AS value FROM
events e1
JOIN
events e2
ON
e1.event_type = e2.event_type
AND
e1.time = (SELECT time FROM events temp1 WHERE
           temp1.event_type=e1.event_type ORDER BY time DESC LIMIT 1)
AND
e2.time = (SELECT time FROM events temp2 WHERE
           temp2.event_type=e2.event_type ORDER BY time DESC LIMIT 1 OFFSET 1)