> and I would like to create a new view that takes the first table and
> calculates the time difference in minutes between each row so that the
> result is something like:
>
> client_id,datetime, previousTime, difftime
> 122,2007-05-01 12:01:00, 2007-05-01 12:00:00, 1
> 455,2007-05-01 12:03:00, 2007-05-01 12:02:00, 1
> 455,2007-05-01 12:08:00, 2007-05-01 12:03:00, 5
> 299,2007-05-01 12:34:00, 2007-05-01 12:10:00, 24
>
> Any idea how I could replicate this in SQL from PG. Would this be an
> easy thing to do in Pl/pgSQL? If so could anyone give any directions
> as to where to start?
You can create a set-returning function, that cursors over the table,
like this:
CREATE OR REPLACE FUNCTION lagfunc(
OUT client_id INT,
OUT datetime timestamp,
OUT previousTime timestamp,
OUT difftime interval)
RETURNS SETOF RECORD as $$
DECLARE
thisrow RECORD;
last_client_id INT;
last_datetime timestamp;
BEGIN
FOR thisrow IN SELECT * FROM all_client_times ORDER BY client_id,
datetime LOOP
IF thisrow.client_id = last_client_id THEN
client_id := thisrow.datetime;
datetime := thisrow.datetime;
previousTime := last_datetime;
difftime = datetime-previousTime;
RETURN NEXT;
END IF;
last_client_id := thisrow.client_id;
last_datetime := thisrow.datetime;
END LOOP;
RETURN;
END;
$$ LANGUAGE plpgsql;
select * from lagfunc() limit 10;
select * from lagfunc() where client_id = 455;
Here I used an interval, but you get the idea.
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