ERROR: timestamp units "timezone" not supported
That's the error I get for all timezone fields.
Here's a minimal query you can run:
select extract(timezone_hour from now()::timestamptz at time zone 'US/Eastern');
What I want is the utc offset in hours. So this should return -4.
The requirement is that I use a dynamic time zone in the query. So I have a table of "facilities" with time zone strings, and I need to get the current time for each one.
So my end query should look something like this:
SELECT
EXTRACT(timezone_hour from now() with time zone timezone) # timezone is the name of the field
FROM facilities;
I thought I had it for a second with this, but this is giving me my current offset, not the offset of the tz I'm passing:
select
extract(timezone_hour from (select now()::timestamp at time zone 'US/Eastern'))
date_part
-----------
-7
I ended up getting this to work with creating two timestamps, one at utc and one at the desired time zone, but I'll leave this open just in case there's a better solution than my current one:
select
extract(hour from (
select (
select now() at time zone 'US/Eastern') - (select now() at time zone 'UTC')));
date_part
-----------
-4
Related
I have a PostgreSQL table named testing with a column named creation_time as timestamp with time zone. The database timezone is UTC
Now I want to get all rows whose time is greater than 00:00 of the current day as per the timezone "America/New_York".
I know how to get all rows after local midnight:
SELECT * FROM testing
WHERE ( creation_time >= now()::date)
ORDER BY id DESC
But how to use this query with a different timezone?
Assuming "the current day" is also defined by NY time, not by the current timezone setting.
SELECT *
FROM testing
WHERE creation_time >= date_trunc('day', now() AT TIME ZONE 'America/New_York') AT TIME ZONE 'America/New_York'
ORDER BY id DESC;
Yes, AT TIME ZONE 'America/New_York' twice. No typo there.
now() AT TIME ZONE 'America/New_York') gets local NY time. date_trunc gets 00:00 of that day. The 2nd AT TIME ZONE 'America/New_York' converts the local time back to timestamptz, which we finally compare to.
If you want NY 00:00 of your local date, it's simpler:
WHERE creation_time >= CURRENT_DATE::timestamp AT TIME ZONE 'America/New_York'
Same time, but can be a different day!
CURRENT_DATE is the local date (date according to the time zone setting of the current session). Effectively the same as now()::date.
Further reading:
Ignoring time zones altogether in Rails and PostgreSQL
I am working with time data that is currently stores in UTC but I want it to be in PST, which is 8 hours behind. I have a pretty lengthy and involved query, but the only thing I am interested in is the time right now so I have included those parts. I want to convert the times to PST and then group by the date for the last week of data. The query has the following structure:
select
date_trunc('day', time1) AT TIME ZONE 'US/Pacific'
...
where
time1 AT TIME ZONE 'US/Pacific' > now() AT TIME ZONE current_setting('TimeZone') - INTERVAL '168 HOURS'
...
group by date_trunc('day', time1)
This results in the following time groupings. From my understanding, it groups from the 0:00 UTC, which is 16:00 in PST. However, I want the groupby to start at 0:00 PST. How do I do this? Right now, the counts in each group are misleading for each day because they go from 4 pm to 4 pm instead of 12 am to 12 am. For example, Sundays have uncharacteristically high counts because Sunday includes part of Monday's data in the groupby. I would appreciate any input to fix this issue. Thank you.
The answer depends on whether it is a timestamp with time zone or one without:
If it's a timestamp with time zone, you can convert to PST with select time1 AT TIME ZONE 'US/Pacific' and get the date with select date_trunc('day', time1 AT TIME ZONE 'US/Pacific')
If it's a timestamp without time zone stored in UTC that you want to convert, you first have to tell PostgreSQL to interpret it as UTC, then convert it, like so: select (time1 AT TIME ZONE 'Z') AT TIME ZONE 'US/Pacific' and of course you can get the date with select date_trunc('day', (time1 AT TIME ZONE 'Z') AT TIME ZONE 'US/Pacific')
In either case you have to convert time zones before truncating to the day level or you may end up with inaccurate results.
I have a column called login_timestamp, which is of type TIMESTAMP WITH TIME ZONE.
To retrieve the month for this timestamp, I would do: EXTRACT(MONTH FROM login_timestamp).
However, I would like to retrieve the month for a specific time zone (in my case, Pakistan), but can't figure out how to do that.
Documentation for this is under Date/Time Functions and Operators. Search that page for "at time zone".
select extract(month from login_timestamp at time zone 'Asia/Karachi');
You can change the time zone for a single session or for a single transaction with set session... or set local.... For example, this changes the time zone for the current session.
set session time zone 'Asia/Karachi';
Use the AT TIME ZONE construct:
SELECT EXTRACT(MONTH FROM login_timestamp AT TIME ZONE '-5');
-5 is the constant offset for Pakistan.
Details:
Ignoring timezones altogether in Rails and PostgreSQL
Try applying AT TIME ZONE. Demo
select extract(month from cast ('2017-07-01 01:00+03' as TIMESTAMP WITH TIME ZONE) AT TIME ZONE '+08') as monthNo
returns
monthno
1 6
I have to compare the two dates to get the last 10 min records from database,I'm using postgresql,
I have write this query
select *
FROM x_table
WHERE x_time >= (NOW()::TIMESTAMP WITHOUT TIME ZONE - interval '10 minutes');
x_time is timestamp without time zone so that's why i'm converting the other to the same but it won't giving the result.
Query should written the last 1 min records but i think due to time zone issue it is not giving the result.
how can i resolve the issue?
If x_time is timestamp without time zone, you should specify proper time zone for NOW() function.
Try
select *FROM x_table WHERE x_time >= (NOW() at time zone '-04' - interval '10 minutes')
What is the best way to add a specified interval to a timestamp with time zone, if I don't want to do the calculation in the time zone of the server. This is particularly important around daylight savings transitions.
e.g.
consider the evening that we "spring forward". (Here in Toronto, I think it was 2016-03-13 at 2am).
If I take a time stamp:
2016-03-13 00:00:00-05
and add '1 day' to it, in Canada/Eastern, I would expect to get 2016-03-14 00:00:00-04 -> 1 day later, but actually only 23 hours
But if I add 1 day to it in Saskatchewan (a place that doesn't use DST), I would want it to add 24 hours, so that I'd end up with
2016-03-13 01:00:00-04.
If I have columns / variables
t1 timestamp with time zone;
t2 timestamp with time zone;
step interval;
zoneid text; --represents the time zone
I essentially want to say
t2 = t1 + step; --in a time zone of my choosing
Postgres documentation seems to indicate that timestamp with time zone is internally stored in UTC time, which seems to indicate that a timestamptz column has no reckoning of a time zone in it.
The SQL standard indicates that
datetime + interval operation should maintain the time zone of the first operand.
t2 = (t1 AT TIME ZONE zoneid + step) AT TIME ZONE zoneid;
doesn't seem to work because the first cast turns t1 into a timezone-less timestamp and thus can't reckon DST transitions
t2 = t1 + step;
doesn't seem to work as it does the operation in the time zone of my SQL server
set the postgres time zone before the operation and change it back after?
A better illustration:
CREATE TABLE timestamps (t1 timestamp with time zone, timelocation text);
SET Timezone 'America/Toronto';
INSERT INTO timestamps(t1, timelocation) VALUES('2016-03-13 00:00:00 America/Toronto', 'America/Toronto');
INSERT INTO timestamps(t1, timelocation) VALUES('2016-03-13 00:00:00 America/Regina', 'America/Regina');
SELECT t1, timelocation FROM timestamps; -- shows times formatted in Toronto time. OK
"2016-03-13 00:00:00-05";"America/Toronto"
"2016-03-13 01:00:00-05";"America/Regina"
SELECT t1 + '1 day', timelocation FROM timestamps; -- Toronto timestamp has advanced by 23 hours. OK. Regina time stamp has also advanced by 23 hours. NOT OK.
"2016-03-14 00:00:00-04";"America/Toronto"
"2016-03-14 01:00:00-04";"America/Regina"
How to get around this?
a) Cast the timestamptz to a timestamp tz in the appropriate time zone?
SELECT t1 AT TIME ZONE timelocation + '1 day', timelocation FROM timestamps; --OK. Though my results are timestamps without time zone now.
"2016-03-14 00:00:00";"America/Toronto"
"2016-03-14 00:00:00";"America/Regina"
SELECT t1 AT TIME ZONE timelocation + '4 hours', timelocation FROM timestamps; -- NOT OK. I want the Toronto time to be 5am
"2016-03-13 04:00:00";"America/Toronto"
"2016-03-13 04:00:00";"America/Regina"
b) Change timezone of postgres and proceed.
SET TIMEZONE = 'America/Regina';
SELECT t1 + '1 day', timelocation FROM timestamps; -- Now the Regina time stamp is correct, but toronto time stamp is incorrect (should be 22:00-06)
"2016-03-13 23:00:00-06";"America/Toronto"
"2016-03-14 00:00:00-06";"America/Regina"
SET TIMEZONE = 'America/Toronto';
SELECT t1 + '1 day', timelocation FROM timestamps; -- toronto is correct, regina is not, as before
"2016-03-14 00:00:00-04";"America/Toronto"
"2016-03-14 01:00:00-04";"America/Regina"
This solution will only work if I continually switch the postgres timezone before every operation time interval operation.
It is a combination of two properties that causes your problem:
timestamp with time zone is stored in UTC and does not contain any time zone information. A better name for it would be “UTC timestamp”.
Addition of timestamp with time zone and interval is always performed in the current time zone, i.e. the one set with the configuration parameter TimeZone.
Since what you really need to store is a timestamp and the time zone in which it is valid, you should store a combination of timestamp without time zone and a text representing the time zone.
As you correctly noticed, you would have to switch the current time zone to perform interval addition over the daylight savings time shift correctly (otherwise PostgreSQL does not know how long 1 day is).
But you don't have to do that by hand, you can use a PL/pgSQL function to do it for you:
CREATE OR REPLACE FUNCTION add_in_timezone(
ts timestamp without time zone,
tz text,
delta interval
) RETURNS timestamp without time zone
LANGUAGE plpgsql IMMUTABLE AS
$$DECLARE
result timestamp without time zone;
oldtz text := current_setting('TimeZone');
BEGIN
PERFORM set_config('TimeZone', tz, true);
result := (ts AT TIME ZONE tz) + delta;
PERFORM set_config('TimeZone', oldtz, true);
RETURN result;
END;$$;
That would give you the following, where the result is to be understood in the same time zone as the argument:
test=> SELECT add_in_timezone('2016-03-13 00:00:00', 'America/Toronto', '1 day');
add_in_timezone
---------------------
2016-03-14 00:00:00
(1 row)
test=> SELECT add_in_timezone('2016-03-13 00:00:00', 'America/Regina', '1 day');
add_in_timezone
---------------------
2016-03-14 00:00:00
(1 row)
test=> SELECT add_in_timezone('2016-03-13 00:00:00', 'America/Toronto', '4 hours');
add_in_timezone
---------------------
2016-03-13 05:00:00
(1 row)
test=> SELECT add_in_timezone('2016-03-13 00:00:00', 'America/Regina', '4 hours');
add_in_timezone
---------------------
2016-03-13 04:00:00
(1 row)
You could consider creating a combined type
CREATE TYPE timestampattz AS (
ts timestamp without time zone,
zone text
);
and define operators and casts on it, but that's probably a major project that exceeds what you want for this.
There even is a PostgreSQL extension timestampandtz that does exactly that; maybe that's just what you need (I didn't look what the semantics for addition are).
Based on the informations given by #LaurenzAlbe, I used something different to handle adding an interval to a timestamptz and using DST. I had the problem this 2020-10-25 since in Belgium (timezone "Europe/Brussels" which is UTC+1) we observe DST and on 2020-10-25 at 03:00 we went backward for 1 hour ending at 02:00, i.e. we went from summer time UTC+2 to winter time UTC+1.
The code below which has to find the timestamptz at 16:00 on a given day failed that day and instead ended at 15:00 because we went backward 1h. The problematic line of code was:
select date_trunc('day', myfct.datetime) + interval 'PT16H'
For example, first query is ok, second is not.
select date_trunc('day', timestamptz '2020-10-27 17:00:00+01') + interval 'PT16H';
?column?
------------------------
2020-10-27 16:00:00+01
select date_trunc('day', timestamptz '2020-10-25 17:00:00+01') + interval 'PT16H';
?column?
------------------------
2020-10-25 15:00:00+01
The idea is to make the addition with a timestamp (without time zone) instead of a timestamptz and finally convert it to a timestamptz with the configured time zone of the database.
hydro_dev=> select date_trunc('day', timestamptz '2020-10-25 17:00:00+01');
date_trunc
------------------------
2020-10-25 00:00:00+02
(1 row)
hydro_dev=> select date_trunc('day', timestamptz '2020-10-25 17:00:00+01')::timestamp;
date_trunc
---------------------
2020-10-25 00:00:00
(1 row)
hydro_dev=> select date_trunc('day', timestamptz '2020-10-25 17:00:00+01')::timestamp + interval 'PT16H';
?column?
---------------------
2020-10-25 16:00:00
(1 row)
select (date_trunc('day', timestamptz '2020-10-25 17:00:00+01')::timestamp + interval 'PT16H')::timestamptz;
timestamptz
------------------------
2020-10-25 16:00:00+01