Sum over a given time period - sql

Question

The following codes gives the total duration that a light has been switched on.
CREATE TABLE switch_times (
id SERIAL PRIMARY KEY,
is1 BOOLEAN,
id_dec INTEGER,
label TEXT,
ts TIMESTAMP WITH TIME ZONE default current_timestamp
);
CREATE VIEW makecount AS
SELECT *, row_number() OVER (PARTITION BY id_dec ORDER BY id) AS count
FROM switch_times;
select c1.label, SUM(c2.ts-c1.ts) AS sum
from
(makecount AS c1
inner join
makecount AS c2 ON c2.count = c1.count + 1)
where c2.is1=FALSE AND c1.id_dec = c2.id_dec AND c2.is1 != c1.is1
GROUP BY c1.label;
Link to working demo https://dbfiddle.uk/ZR8pLEBk
Any suggestions on how to alter the code so that it would give the sum over a given specific time period, say the 25th, during which all three lights were switched on for 12 hours? Problem 1: current code gives total sum, as follows. Problem 2: all durations that have not ended are disregarded, because there is no switch off time.
label sum
0x29 MH3 1 day 03:00:00
0x2B MH1 1 day 01:00:00
0x2C MH2 1 day 02:00:00
The expected results is just over a a given date, i.e.
label sum
0x29 MH3 12:00:00
0x2B MH1 12:00:00
0x2C MH2 12:00:00

Answer 1

Assuming the following (which should be defined in the question):
Postgres 15.
The table is big, many rows per label, performance matters, we can add indexes.
All columns are actually NOT NULL, you just forgot to declare columns as such.
Evey "light" has a distinct id_dec and a distinct label. Having both in switch_times is redundant. (Normalization!)
A light is "switched on" if the most recent earlier entry has is1 IS TRUE. Else it's considered "off".
The order of rows is established by ts, not by id as used in your query (typically incorrect).
Consecutive entries do not have to change the state.
No duplicate entries for (id_dec, ts). (There is a unique index enforcing that.)
There is no minimum or maximum time interval between entries.
"The 25th" is supposed to mean tstzrange '[2022-11-25 0:0+02, 2022-11-26 0:0+02)' (Note the time zone offsets.)
You want results for all labels that were switched on at all during the given time interval.
There is a table "labels" with one distinct entry per relevant light. If you don't have one, create it.
Indexes
Have at least these indexes to make everything fast:
CREATE INDEX ON switch_times (id_dec, ts DESC);
CREATE INDEX ON switch_times (ts);
Optional step to create table labels
CREATE TABLE labels AS
WITH RECURSIVE cte AS (
(
SELECT id_dec, label
FROM switch_times
ORDER BY 1
LIMIT 1
)
UNION ALL
(
SELECT s.id_dec, s.label
FROM cte c
JOIN switch_times s ON s.id_dec > c.id_dec
ORDER BY 1
LIMIT 1
)
)
TABLE cte;
ALTER TABLE labels
ADD PRIMARY KEY (id_dec)
, ALTER COLUMN label SET NOT NULL
, ADD CONSTRAINT label_uni UNIQUE (label)
;
Why this way? See:
Optimize GROUP BY query to retrieve latest row per user
Main query
WITH bounds(lo, hi) AS (
SELECT timestamptz '2022-11-25 0:0+02' -- enter time interval here *once*
, timestamptz '2022-11-26 0:0+02'
)
, snapshot AS (
SELECT id_dec, label, is1, ts
FROM switch_times s, bounds b
WHERE s.ts >= b.lo
AND s.ts < b.hi
UNION ALL -- must be separate
SELECT s.*
FROM labels l
JOIN LATERAL ( -- latest earlier entry
SELECT s.id_dec, s.label, s.is1, b.lo AS ts -- cut off at lower bound
FROM switch_times s, bounds b
WHERE s.id_dec = l.id_dec
AND s.ts < b.lo
ORDER BY s.ts DESC
LIMIT 1
) s ON s.is1 -- ... if it's "on"
)
SELECT label, sum(z - a) AS duration
FROM (
SELECT label
, lag(is1, 1, false) OVER w AS last_is1
, lag(ts) OVER w AS a
, ts AS z
FROM snapshot
WINDOW w AS (PARTITION BY label ORDER BY ts ROWS UNBOUNDED PRECEDING)
) sub
WHERE last_is1
GROUP BY 1;
fiddle
CTE bounds is an optional convenience feature to enter lower and upper bound of your time interval once.
CTE snapshot collects all rows of interest, which consists of
all rows inside the time interval (1st leg of UNION ALL query)
the latest earlier row if it was "on" (2nd leg of UNION ALL query)
We need to gather 2. separately to cover corner cases where the light was switched on earlier and there is no entry for the given time interval! But we can replace the timestamp to the lower bound immediately.
The final query gets the previous (is1, ts) for every row in a subquery, defaulting to "off" if there was no previous row.
Finally sum up intervals in the outer SELECT. Only sum what's switched on at the begin (no matter the final state).
Related:
Jump SQL gap over specific condition & proper lead() usage

Answer 2

My assumption
actual on time is time difference between is1 is true to next is1 false order by ts
Below query will calculate total sum of on time between two dates
select
id_dec ,
label,
sum(to_timestamp(nexttime)-ts) as time_def
from
(
select
id_dec,
"label",
ts,
is1,
case
when is1 = true then lead(extract(epoch from ts))over(partition by id_dec
order by
id_dec ,
ts asc)
else 0
end nexttime
from
switch_times
where
ts between '2022-11-24' and '2022-11-28'
) as a
where
nexttime <> 0
group by
id_dec,
label