Window function example

query.sql

truncate table events;
CREATE TABLE events(ref_id integer, event_type text, ts integer);
INSERT INTO events (ref_id, event_type, ts) VALUES (1, 'foo', 1), (1, 'bar', 1), (2, 'foo', 0), (3, 'foo', 0), (1, 'foo', 4), (3, 'foo', 7), (2, 'bar', 10);

select
  ref_id,
  event_type,
  ts,
  first_value(ts) over (
    partition by ref_id, event_type order by ts asc rows between 1 following and unbounded following
  ) - ts as delta
from events
where event_type = 'foo'
order by ts

rows.csv