我认为插入前触发器效果很好。您可以创建 before_insert 触发器并在使用先前的引用插入时更新增量 soc。
CREATE TABLE batteries ( time timestamp not null, batt_uid varchar, charge int, delta int);
SELECT create_hypertable('batteries', 'time');
CREATE OR REPLACE FUNCTION update_delta() RETURNS trigger AS
$BODY$
DECLARE
previous_charge integer;
BEGIN
select charge
into previous_charge
from batteries where batt_uid = NEW.batt_uid
order by time desc limit 1;
IF NEW.charge IS NOT NULL THEN
IF previous_charge IS NOT NULL THEN
NEW.delta = NEW.charge - previous_charge;
ELSE
NEW.delta = 0;
END IF;
END IF;
RETURN NEW;
END;
$BODY$
LANGUAGE plpgsql;
CREATE TRIGGER update_delta_on_insert
BEFORE INSERT
ON batteries
FOR EACH ROW
EXECUTE PROCEDURE update_delta();
Testing
INSERT INTO batteries VALUES
('2021-08-26 10:09:00'::timestamp, 'battery-1', 32),
('2021-08-26 10:09:01'::timestamp, 'battery-1', 34),
('2021-08-26 10:09:02'::timestamp, 'battery-1', 38);
INSERT INTO batteries VALUES
('2021-08-26 10:09:00'::timestamp, 'battery-2', 0),
('2021-08-26 10:09:01'::timestamp, 'battery-2', 4),
('2021-08-26 10:09:02'::timestamp, 'battery-2', 28),
('2021-08-26 10:09:03'::timestamp, 'battery-2', 32),
('2021-08-26 10:09:04'::timestamp, 'battery-2', 28);
输出来自:
SELECT * FROM batteries;
┌─────────────────────┬───────────┬────────┬───────┐
│ time │ batt_uid │ charge │ delta │
├─────────────────────┼───────────┼────────┼───────┤
│ 2021-08-26 10:09:00 │ battery-1 │ 32 │ 0 │
│ 2021-08-26 10:09:01 │ battery-1 │ 34 │ 2 │
│ 2021-08-26 10:09:02 │ battery-1 │ 38 │ 4 │
│ 2021-08-26 10:09:00 │ battery-2 │ 0 │ 0 │
│ 2021-08-26 10:09:01 │ battery-2 │ 4 │ 4 │
│ 2021-08-26 10:09:02 │ battery-2 │ 28 │ 24 │
│ 2021-08-26 10:09:03 │ battery-2 │ 32 │ 4 │
│ 2021-08-26 10:09:04 │ battery-2 │ 28 │ -4 │
└─────────────────────┴───────────┴────────┴───────┘