Postgres: difference between two timestamps (hours:minutes:seconds) - postgresql

Question

i'm creating a select that calculate the difference between two timestamps
here the code: (isn't necessary you understand tables below. Just follow the thread)
(select value from demo.data where id=q.id and key='timestampend')::timestamp
- (select value from demo.data where id=q.id and key='timestampstart')::timestamp) as durata
Look at this example, if you want easier:
select timestamp_end::timestamp - timestamp_start as duration
here the result:
// "durata" is duration
The problem is that the first timestamp is 2017-06-21 and the second is 2017-06-22 so we have 1 day and some hours of difference.
How can i do for show the result not like "1 day 02:06:41.993657" but "26:06:41.993657" without milliseconds (26:06:41)?
Update
I'm testing this query:
select id as ticketid,
(select value from demo.data where id=q.id and key = 'timestampstart')::timestamp as TEnd,
(select value from demo.data where id=q.id and key = 'timestampend')::timestamp as TStart,
(select
make_interval
(
0,0,0,0, -- years, months, weeks, days
extract(days from duration1)::int * 24 + extract(hours from duration1)::int, -- calculated hours (days * 24 + hours)
extract(mins from duration1)::int, -- minutes
floor(extract(secs from duration1))::int -- seconds, without miliseconds, thus FLOOR()
) as duration1
from
(
(select value from demo.data where id=q.id and key='timestampstart')::timestamp - (select value from demo.data where id=q.id and key='timestampend')::timestamp
) t(duration) as dur
from (select distinct id from demo.data) q
error is the same: [Err] ERROR: syntax error at or near "::"
there is an error on id = q.id
data table is like this:

Answer 1

You could use EXTRACT function and wrap it up with MAKE_INTERVAL and some math. It's pretty straight forward, since you pass each part of timestamp to it:
select
make_interval(
0,0,0,0, -- years, months, weeks, days
extract(days from durdata)::int * 24 + extract(hours from durdata)::int, -- calculated hours (days * 24 + hours)
extract(mins from durdata)::int, -- minutes
floor(extract(secs from durdata))::int -- seconds, without miliseconds, thus FLOOR()
) as durdata
from (
select '2017-06-22 02:06:41.993657'::timestamp - '2017-06-21'::timestamp
) t(durdata);
Output:
durdata
----------
26:06:41
You could wrap it up within a function to make it easy to work with.
There is no worry about timestamp - timestamp returning an output with precision to more than days, and thus losing you some information, because even calculation for different years would still return days and additional time part.
Example:
postgres=# select ('2019-06-22 01:03:05.993657'::timestamp - '2017-06-21'::timestamp) as durdata;
durdata
------------------------
731 days 01:03:05.993657

Answer 2

In Postgres, although interval data type allows having hours value greater than 23 (see https://www.postgresql.org/docs/9.6/static/functions-formatting.html), to_char() function will cut out days and will take only "hours within a day" if you put delta value to it and try to get 'HH24' value.
So, I ended up with such trick, combining to_char(...) with extract('epoch' from...) and then putting the concatinated value to another to_char():
with timestamps(ts1, ts2) as (
select
'2017-06-21'::timestamptz,
'2017-06-22 01:03:05.1212'::timestamptz
), res as (
select
round(extract('epoch' from ts2 - ts1) / 3600) as hours,
to_char(ts2 - ts1, 'MI:SS') as min_sec
from timestamps
)
select hours, min_sec, to_char(format('%s:%s', hours, min_sec)::interval, 'HH24:MI:SS')
from res;
The result is:
hours | min_sec | to_char
-------+---------+----------
25 | 03:05 | 25:03:05
(1 row)
You can define an SQL function to make using it easier:
create or replace function extract_hhmmss(timestamptz, timestamptz) returns interval as $$
with delta(i) as (
select
case when $2 > $1 then $2 - $1
else $1 - $2
end
), res as (
select
round(extract('epoch' from i) / 3600) as hours,
to_char(i, 'MI:SS') as min_sec
from delta
)
select
(
case when $2 < $1 then '-' else '' end
|| to_char(format('%s:%s', hours, min_sec)::interval, 'HH24:MI:SS')
)::interval
from res;
$$ language sql stable;
Example of usage:
[local]:5432 nikolay#test=# select extract_hhmmss('2017-06-21'::timestamptz, '2017-06-22 01:03:05.1212'::timestamptz);
extract_hhmmss
----------------
25:03:05
(1 row)
Time: 0.882 ms
[local]:5432 nikolay#test=# select extract_hhmmss('2017-06-22 01:03:05.1212'::timestamptz, '2017-06-21'::timestamptz);
extract_hhmmss
----------------
-25:03:05
(1 row)
Notice, that it will give an error if timestamps are provided in reverse order, but it's not really hard to fix. // Update: already fixed.