I store timestamps with time zone in my postgres database. The server time zone is UTC. All the timestamptzs are stored as UTC datetimes.
Now, I'd like to retrieve those timestamps, but for a specific time zone (e.g. US/Pacific). Because of daylight savings time, the correct time zone is sometimes PDT and sometimes PST. So I can't just run a query like select t at time zone 'pdt' because this will be wrong for the pst dates.
Is there a way to pull the dates from the database in the correct time zone?
According to the documentation, together with TIME ZONE code you can also specify locales. For your case you can use something like that:
ds=# SELECT current_setting('TIMEZONE');
current_setting
-----------------
UTC
(1 row)
ds=# SELECT now();
now
-------------------------------
2015-11-05 00:35:03.126317+00
(1 row)
pm7=# SELECT now() AT TIME ZONE 'America/Los_Angeles';
timezone
----------------------------
2015-11-04 16:35:06.344367
(1 row)
Related
I have one server which is on UTC time and one which is on EST. Now I dumped the database from the UTC one and imported it to the EST one. As timestamps are always saved as UTC I cannot find a reason the reason I get two different results for the same query:
select reported_on at time zone 'UTC', temperature from data order by reported_on desc;
UTC Server:
temperature | device | timezone
-------------+--------------------------------------+----------------------------
17.2 | ------------------------------------ | 2020-05-05 12:13:16.256+00
EST Server:
temperature | device | timezone
-------------+--------------------------------------+----------------------------
17.2 | ------------------------------------ | 2020-05-05 14:13:16.256+02
What am I missing here? How can I query the data without the timezones, I need the UTC time, not the +02 time? How can I achieve this?
Edit:
I added the lines through nodejs:
INSERT INTO data(device, reported_on, temperature, humidity) VALUES($1, to_timestamp(' + Date.now() /1000.0 + '), $2, $3) RETURNING *
The Typ of the column is:
reported_on TIMESTAMP,
Update:
Altering the timezone fixed the issue!
ALTER DATABASE sensors SET timezone TO 'UTC';
SELECT pg_reload_conf();
This is about your local database configuration. I created a dummy database locally and the result was this:
test=# CREATE TABLE timestamptest (timezone TIMESTAMPTZ);`
Showed my timezone pattern:
test=# SHOW TIMEZONE;
TimeZone
----------
UTC
(1 row)
And inserted some values inside:
test=# SELECT * FROM timestamptest;
timezone
-------------------------------
2020-05-05 15:26:27.377549+00
2020-05-05 15:28:14.014597+00
(2 rows)
Now, I changed the local timezone variable:
test=# SET TIME ZONE 'America/Montreal';
SET
And selected the info again:
test=# INSERT INTO timestamptest VALUES (now());
INSERT 0 1
test=# SELECT * FROM timestamptest ;
timezone
-------------------------------
2020-05-05 11:26:27.377549-04
2020-05-05 11:28:14.014597-04
(2 rows)
And my timezone is different because the SET command:
test=# SHOW timezone;
TimeZone
------------------
America/Montreal
(1 row)
You can change your local configuration and, about your selects showed in your question, the import seems to be correct, just the local timestamp configuration needed to be set equals from one to another.
Note that -04 on the end of the timestamp shows that your time has changed 4 hours in relation of -00 originally. Just a formatting ouptut.
More information here: here on postgresql docs
The statement "timestamps are always saved as UTC" is incorrect. Timestamp without time (timestamp) is stored with local time, timestamp with time zone (timestamptz) is always stored in UTC. From the documentation:
timestamp without time zone, PostgreSQL will silently ignore any time
zone indication. That is, the resulting value is derived from the
date/time fields in the input value, and is not adjusted for time
zone.
For timestamp with time zone, the internally stored value is always in
UTC (Universal Coordinated Time, traditionally known as Greenwich Mean
Time, GMT). An input value that has an explicit time zone specified is
converted to UTC using the appropriate offset for that time zone. If
no time zone is stated in the input string, then it is assumed to be
in the time zone indicated by the system's TimeZone parameter, and is
converted to UTC using the offset for the timezone zone.
Additional be very careful using 'EST', or any of the other timezone abbreviations, instead use the full timezone name. The abbreviations indicate a fixed UTC offset (i.e. EST is always UTC-5, and EDT is always UTC-4) and do not recognize Daylight Savings Time (DST). On the other hand the full names (i.e. are US/Central' or 'America/Montreal' or any other full timezone name) are DST aware and adjust UTC offset accordingly.
Unlike the abbreviations shown in pg_timezone_abbrevs, many of these
names imply a set of daylight-savings transition date rules.
You can observe this with:
select * from pg_timezone_abbrevs where abbrev in ('EDT', 'EST')
select * from pg_timezone_names where name in ('US/Eastern','America/New_York','America/Montreal')
The type of the column is TIMESTAMP*"
I guess there's your problem. You'll want to use TIMESTAMP WITH TIME ZONE instead. Alternatively, do not use AT TIME ZONE 'UTC' in your SELECT statement, so that you just get back the same timestamp that was stored, regardless of timezone.
What is happening in SELECT reported_on AT TIME ZONE 'UTC' is that the stored date is converted from the database's local timezone to UTC. In your second database with a different local timezone, that's a different conversion, leading to the offset in the result.
I have a single timestamptz that I want to date_trunc so it removes the hours:
2019-01-01T17:43-03 => 2019-01-01T00:00-03.
However, because date_trunc removes the timezone, I need to do it like this:
date_trunc('day', '2019-01-01T17:43-03'::timestamptz) at time zone '-03'
However, I do not want to hardcode the time zone, since the query is run with timestamptz in many different timezones (these are input to the query and not stored). So I want the timezone to be extracted from the original timestamp. I tried to do something like this, but it does not work:
date_trunc('day', '2019-01-01T17:43-03'::timestamptz) at time zone EXTRACT(...)
Related, I am trying to extract the timezone from a timestamptz, but just getting 0.
SELECT EXTRACT(timezone FROM TIMESTAMP WITH TIME ZONE '2019-01-01T00:00+03')
0
Can anybody help me with this?
I believe you may have a misconception about how timestamps and timezones are stored in PostgreSQL (because you seem to expect the -03 to be preserved when calling date_trunc and that you "want the timezone to be extracted from the original timestamp"). According to the documentation:
When a timestamp with time zone value is output, it is always converted from UTC to the current timezone zone, and displayed as local time in that zone. To see the time in another time zone, either change timezone or use the AT TIME ZONE construct (see Section 9.9.3).
Therefore, the statement that "different clients [that] have timestampts in many different timezones," while true, are all translated to UTC for storage, and then displayed in your local timezone (or the timezone you specify) for output. As such, calling date_trunc() will essentially truncate the UTC timestamp, and if you want it displayed in a specific timezone, you will need to add the AT TIME ZONE clause.
UPDATE: An example is here:
edb=# select date_trunc('day', '2019-01-01T17:43-03'::timestamptz) ;
date_trunc
------------------------
2019-01-01 00:00:00+00
(1 row)
edb=# set timezone to 'US/Pacific';
SET
edb=# select date_trunc('day', '2019-01-01T17:43-03'::timestamptz) ;
date_trunc
------------------------
2019-01-01 00:00:00-08
(1 row)
As you can see, date_trunc will append the timezone that I define—it is not omitted.
I have to read strings like '20190608070000' as timestamps given in UTC. Is there an easy way to do that?
This one takes UTC but needs formatted input:
postgres=# show time zone;
TimeZone
----------
CET
(1 Zeile)
postgres=# select timestamp without time zone '2019-06-08 07:00:00' at time zone 'UTC';
timezone
------------------------
2019-06-08 09:00:00+02
(1 Zeile)
Whereas to_timestamp() invariably treats all input as local time as far as I see, so the output is shifted the wrong way:
postgres=# SELECT to_timestamp('20190608070000', 'YYYYMMDDHH24MISS') AT time zone 'UTC';
timezone
---------------------
2019-06-08 05:00:00
(1 Zeile)
Actually I'm using PostgreSQL 9.6.
The return type of TO_TIMESTAMP is timestamp with time zone. The time shown is in your current session's time zone(with the UTC offset).
SET SESSION timezone TO 'CET';
SET
knayak=# SELECT to_timestamp('20190608070000', 'YYYYMMDDHH24MISS');
to_timestamp
------------------------
2019-06-08 07:00:00+02
When you transform it with AT TIME ZONE, it will show the time in UTC when it's 07:00 hours in your current time zone.
SELECT to_timestamp('20190608070000', 'YYYYMMDDHH24MISS') AT time zone 'UTC';
timezone
---------------------
2019-06-08 05:00:00
(1 row)
So, If you wish to read your timestamp in a desired format and treat that as UTC, cast the output of to_timestamp explicitly to timestamp (without time zone) and then apply AT TIME ZONE.
SELECT to_timestamp('20190608070000', 'YYYYMMDDHH24MISS') :: timestamp
AT time zone 'UTC';
timezone
------------------------
2019-06-08 09:00:00+02
(1 row)
I am new to PostgreSQL and I was wondering if there is a direct way to just convert the timestamp values in a table to a different timezone using a function. In my case it is UTC to EST.
These are the values for example that I need to convert to EST (not just one value but all the values in the table)
date
-------------------
2015-10-24 16:38:46
2016-01-19 18:27:00
2016-01-24 16:14:34
2016-02-09 23:05:49
2016-02-11 20:46:26
Here in London, we are currently 1 hour ahead of UTC. So - if I take your timezone without timestamp and say it is in UTC I will get it printed for my local timezone.
richardh=> SELECT ((timestamp '2015-10-24 16:38:46') AT TIME ZONE 'UTC');
timezone
------------------------
2015-10-24 17:38:46+01
(1 row)
But you want "EST" which seems to be somewhere in the Americas, judging by the value returned. You can wrap the expression in a little SQL function if you wanted to.
richardh=> SELECT ((timestamp '2015-10-24 16:38:46') AT TIME ZONE 'UTC') AT TIME ZONE 'EST';
timezone
---------------------
2015-10-24 11:38:46
(1 row)
Edit: how to do it in a query
SELECT ((stored_timestamp AT TIME ZONE 'UTC') AT TIME ZONE 'EST') AS local_timestamp
FROM my_table;
Similarly
execute
SELECT '2015-10-24 16:38:46'::timestamp AT time zone 'EST';
timezone
------------------------
2015-10-24 21:38:46+00
(1 row)
I usually leave everything in UTC and convert when it is time to show.
I use something like:
SELECT my_date_utc AT time zone 'utc' at time zone 'est' From ....
If you have problem accessing with your zone, you can simply pass your zone interval also.
To convert timestamp from IST to UTC.
SELECT '2020-12-14 06:38:46'::timestamp AT time zone INTERVAL '+05:30';
timezone
------------------------
2015-10-24 11:38:46+00
(1 row)
To convert timestamp from UTC to IST.
SELECT '2020-12-14 06:38:46'::timestamp AT time zone INTERVAL '-05:30';
timezone
------------------------
2020-12-14 12:08:46+00
(1 row)
It is 12:22 here in Los Angeles now.
I find that I have to reverse the UST and america/los_angeles arguments:
ods=> SELECT NOW(),(NOW() AT TIME ZONE 'america/los_angeles') AT TIME ZONE 'utc';;
now | timezone
-------------------------------+-------------------------------
2022-04-22 19:22:35.943605+00 | 2022-04-22 12:22:35.943605+00
(1 row)
Am I missing something?
You should always store the main reference of a date in UTC and either convert it to a time zone in your queries or store the specific timezone version of the data in another column. The reason for this is that it is quick and easy to convert a date from UTC to another time zone as long as you know that the timezone that it is stored as is UTC. It takes the guess work out of it. Alternatively, you can store the date WITH the timezone.
If you have an operation that automatically populates the date with the system clock of your server, then you can either
A: Change the operation to use UTC time
B: Change the system clock on the server to UTC
I had the same problem, I am working with different regions and timezones, I need to just fix the timezone in the query the way it doesn't effect other customers around the regions and I havent changed the table structure or any thing(Open–closed principle) . What I did In my query:
SELECT TO_CHAR(current_timestamp at time zone 'Australia/Melbourne', 'DD/MM/YYYY hh24:mi AM') as date_of_extract
This worked for me and I could change the 'UTC' defult timezone for my postgressql to the 'Australia/Melbourne'(any time zone you are looking into). hope this is helpful.
Building off of #Leandro Castro's answer...
To get current time in in timezone, use the CURRENT_TIME function:
SELECT CURRENT_TIME(0) AT time zone 'utc' at time zone 'est';
Are timestamp values stored differently in PostgreSQL when the data type is WITH TIME ZONE versus WITHOUT TIME ZONE? Can the differences be illustrated with simple test cases?
The differences are covered at the PostgreSQL documentation for date/time types. Yes, the treatment of TIME or TIMESTAMP differs between one WITH TIME ZONE or WITHOUT TIME ZONE. It doesn't affect how the values are stored; it affects how they are interpreted.
The effects of time zones on these data types is covered specifically in the docs. The difference arises from what the system can reasonably know about the value:
With a time zone as part of the value, the value can be rendered as a local time in the client.
Without a time zone as part of the value, the obvious default time zone is UTC, so it is rendered for that time zone.
The behaviour differs depending on at least three factors:
The timezone setting in the client.
The data type (i.e. WITH TIME ZONE or WITHOUT TIME ZONE) of the value.
Whether the value is specified with a particular time zone.
Here are examples covering the combinations of those factors:
foo=> SET TIMEZONE TO 'Japan';
SET
foo=> SELECT '2011-01-01 00:00:00'::TIMESTAMP;
timestamp
---------------------
2011-01-01 00:00:00
(1 row)
foo=> SELECT '2011-01-01 00:00:00'::TIMESTAMP WITH TIME ZONE;
timestamptz
------------------------
2011-01-01 00:00:00+09
(1 row)
foo=> SELECT '2011-01-01 00:00:00+03'::TIMESTAMP;
timestamp
---------------------
2011-01-01 00:00:00
(1 row)
foo=> SELECT '2011-01-01 00:00:00+03'::TIMESTAMP WITH TIME ZONE;
timestamptz
------------------------
2011-01-01 06:00:00+09
(1 row)
foo=> SET TIMEZONE TO 'Australia/Melbourne';
SET
foo=> SELECT '2011-01-01 00:00:00'::TIMESTAMP;
timestamp
---------------------
2011-01-01 00:00:00
(1 row)
foo=> SELECT '2011-01-01 00:00:00'::TIMESTAMP WITH TIME ZONE;
timestamptz
------------------------
2011-01-01 00:00:00+11
(1 row)
foo=> SELECT '2011-01-01 00:00:00+03'::TIMESTAMP;
timestamp
---------------------
2011-01-01 00:00:00
(1 row)
foo=> SELECT '2011-01-01 00:00:00+03'::TIMESTAMP WITH TIME ZONE;
timestamptz
------------------------
2011-01-01 08:00:00+11
(1 row)
I try to explain it more understandably than the referred PostgreSQL documentation.
Neither TIMESTAMP variants store a time zone (or an offset), despite what the names suggest. The difference is in the interpretation of the stored data (and in the intended application), not in the storage format itself:
TIMESTAMP WITHOUT TIME ZONE stores local date-time (aka. wall calendar date and wall clock time). Its time zone is unspecified as far as PostgreSQL can tell (though your application may knows what it is). Hence, PostgreSQL does no time zone related conversion on input or output. If the value was entered into the database as '2011-07-01 06:30:30', then no mater in what time zone you display it later, it will still say year 2011, month 07, day 01, 06 hours, 30 minutes, and 30 seconds (in some format). Also, any offset or time zone you specify in the input is ignored by PostgreSQL, so '2011-07-01 06:30:30+00' and '2011-07-01 06:30:30+05' are the same as just '2011-07-01 06:30:30'.
For Java developers: it's analogous to java.time.LocalDateTime.
TIMESTAMP WITH TIME ZONE stores a point on the UTC time line. How it looks (how many hours, minutes, etc.) depends on your time zone, but it always refers to the same "physical" instant (like the moment of an actual physical event). The
input is internally converted to UTC, and that's how it's stored. For that, the offset of the input must be known, so when the input contains no explicit offset or time zone (like '2011-07-01 06:30:30') it's assumed to be in the current time zone of the PostgreSQL session, otherwise the explicitly specified offset or time zone is used (as in '2011-07-01 06:30:30+05'). The output is displayed converted to the current time zone of the PostgreSQL session.
For Java developers: It's analogous to java.time.Instant (with lower resolution though), but with JDBC and JPA 2.2 you are supposed to map it to java.time.OffsetDateTime (or to java.util.Date or java.sql.Timestamp of course).
Some say that both TIMESTAMP variations store UTC date-time. Kind of, but it's confusing to put it that way in my opinion. TIMESTAMP WITHOUT TIME ZONE is stored like a TIMESTAMP WITH TIME ZONE, which rendered with UTC time zone happens to give the same year, month, day, hours, minutes, seconds, and microseconds as they are in the local date-time. But it's not meant to represent the point on the time line that the UTC interpretation says, it's just the way the local date-time fields are encoded. (It's some cluster of dots on the time line, as the real time zone is not UTC; we don't know what it is.)
Here is an example that should help. If you have a timestamp with a timezone, you can convert that timestamp into any other timezone. If you haven't got a base timezone it won't be converted correctly.
SELECT now(),
now()::timestamp,
now() AT TIME ZONE 'CST',
now()::timestamp AT TIME ZONE 'CST'
Output:
-[ RECORD 1 ]---------------------------
now | 2018-09-15 17:01:36.399357+03
now | 2018-09-15 17:01:36.399357
timezone | 2018-09-15 08:01:36.399357
timezone | 2018-09-16 02:01:36.399357+03
Timestamptz vs Timestamp
The timestamptz field in Postgres is basically just the timestamp field where Postgres actually just stores the “normalised” UTC time, even if the timestamp given in the input string has a timezone.
If your input string is: 2018-08-28T12:30:00+05:30 , when this timestamp is stored in the database, it will be stored as 2018-08-28T07:00:00.
The advantage of this over the simple timestamp field is that your input to the database will be timezone independent, and will not be inaccurate when apps from different timezones insert timestamps, or when you move your database server location to a different timezone.
To quote from the docs:
For timestamp with time zone, the internally stored value is always in
UTC (Universal Coordinated Time, traditionally known as Greenwich Mean
Time, GMT). An input value that has an explicit time zone specified is
converted to UTC using the appropriate offset for that time zone. If
no time zone is stated in the input string, then it is assumed to be
in the time zone indicated by the system’s TimeZone parameter, and is
converted to UTC using the offset for the timezone zone. To give a
simple analogy, a timestamptz value represents an instant in time, the
same instant for anyone viewing it. But a timestamp value just
represents a particular orientation of a clock, which will represent
different instances of time based on your timezone.
For pretty much any use case, timestamptz is almost always a better choice. This choice is made easier with the fact that both timestamptz and timestamp take up the same 8 bytes of data.
source:
https://hasura.io/blog/postgres-date-time-data-types-on-graphql-fd926e86ee87/
The diffrences are shown in PostgreSQL official docs. Please refer the docs for deep digging.
In a nutshell TIMESTAMP WITHOUT TIME ZONE doesn't save any timezone related informations if you give date time with timezone info,it takes date & time only and ignores timezone
For example
When I save this 12:13, 11 June 2021 IST to PostgreSQL TIMESTAMP WITHOUT TIME ZONE will reject the timezone information and saves the date time 12:13,11 June 2021
But the the case of TIMESTAMP WITH TIME ZONE it saves the timezone info in UTC format.
For example
When I save this 12:13, 11 June 2021 IST to PostgreSQL TIMESTAMP WITH TIME ZONE type variable it will interpret this time to UTC value and
stored as shown in below 6:43,11 June 2021 UTC
NB : UTC + 5.30 is IST
During the time conversion time returned by TIMESTAMP WITH TIME ZONE will be stored in UTC format and we can convert it to the required timezone like IST or PST etc.
So the recommented timestamp type in PostgreSQL is TIMESTAMP WITH TIME ZONE or TIMESTAMPZ
Run the following to see diff in pgAdmin:
create table public.testts (tz timestamp with time zone, tnz timestamp without time zone);
insert into public.testts values(now(), now());
select * from public.testts;
If you have similar issues I had of timestamp precision in Angular / Typescript / Node API / PostgreSql environment, hope my complete answer and solution will help you out.