问使用sql，根据条件查找上一行。

EN

select * from (
  select `id`, `user_id`, `event`, `created_at`,
    date(created_at) as date,
    SEC_TO_TIME(TIMESTAMPDIFF(SECOND, created_at, LEAD(created_at) OVER (PARTITION BY user_id ORDER BY created_at))) as duration,
    LAG(event,2) OVER (PARTITION BY user_id ORDER BY created_at)  AS previous_event,
    CASE
        WHEN event = 'subscribe' and LAG(event,2) OVER (PARTITION BY user_id ORDER BY created_at) = 'away' THEN 'away'
        WHEN event = 'subscribe' and LAG(event,2) OVER (PARTITION BY user_id ORDER BY created_at) = 'online' THEN 'online'
        WHEN event = 'subscribe' and LAG(event,2) OVER (PARTITION BY user_id ORDER BY created_at) IS NULL THEN 'online'
        ELSE event END as status
    from `user_websocket_events` where event in ('online','away','unsubscribe','subscribe') and created_at between '2022-04-06 00:00:00' and '2022-04-07 23:59:59' and user_id in(19)
  ) as `Developer`
where created_at between '2022-04-06 00:00:00' and '2022-04-06 23:59:59';

#data for testing
INSERT INTO user_websocket_events (id, user_id, event) VALUES (9606, 19, 'subscribe');
INSERT INTO user_websocket_events (id, user_id, event) VALUES (9609, 19, 'unsubscribe');
INSERT INTO user_websocket_events (id, user_id, event) VALUES (9610, 19, 'subscribe');
INSERT INTO user_websocket_events (id, user_id, event) VALUES (9611, 19, 'away');
INSERT INTO user_websocket_events (id, user_id, event) VALUES (9613, 19, 'unsubscribe');
INSERT INTO user_websocket_events (id, user_id, event) VALUES (9614, 19, 'subscribe');
INSERT INTO user_websocket_events (id, user_id, event) VALUES (9616, 19, 'unsubscribe');
INSERT INTO user_websocket_events (id, user_id, event) VALUES (9618, 19, 'subscribe');
INSERT INTO user_websocket_events (id, user_id, event) VALUES (9634, 19, 'online');
INSERT INTO user_websocket_events (id, user_id, event) VALUES (9635, 19, 'unsubscribe');
INSERT INTO user_websocket_events (id, user_id, event) VALUES (9636, 19, 'subscribe');
INSERT INTO user_websocket_events (id, user_id, event) VALUES (9637, 19, 'unsubscribe');
INSERT INTO user_websocket_events (id, user_id, event) VALUES (9638, 19, 'subscribe');
INSERT INTO user_websocket_events (id, user_id, event) VALUES (9639, 19, 'unsubscribe');
INSERT INTO user_websocket_events (id, user_id, event) VALUES (9640, 19, 'subscribe');
INSERT INTO user_websocket_events (id, user_id, event) VALUES (9641, 19, 'away');
INSERT INTO user_websocket_events (id, user_id, event) VALUES (9642, 19, 'unsubscribe');
INSERT INTO user_websocket_events (id, user_id, event) VALUES (9643, 19, 'subscribe');