Postgres difference between time stamp in minutes, PostgreSQL

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--PostgreSQL 9.6
--'\\' is a delimiter

drop table if exists events;

create table events(
    nodeid     text      not null,
    code       int       not null,
    event_time timestamp not null,
    primary key (nodeid, code, event_time)
);

insert into events(nodeid, code, event_time)
values ('CAI0015', 14961045, '2017-04-22 21:22:00'),
       ('CAI0024', 14961045, '2017-04-23 19:44:00'),
       ('CAI0024', 14961045, '2017-04-23 09:07:00'),
       ('CAI0040', 14971047, '2017-04-23 13:58:00'),
       ('CAI0046', 14961045, '2017-04-23 11:19:00'),
       ('CAI0050', 14961045, '2017-04-24 02:06:00'),
       ('CAI0024', 14961045, '2017-04-24 23:00:00');

select nodeid, code, extract(epoch from e2.event_time - e1.event_time) / 60 difference
from   events e1
join   events e2 using (nodeid, code)
where  e1.event_time < e2.event_time;

select nodeid, code, extract(epoch from event_time - lag) / 60 difference
from   (select *, lag(event_time) over (partition by nodeid, code order by event_time)
        from   events) e
where  lag is not null;


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