I try to deploy a JS application using TypeORM and Postgres on a host. Locally I had a Postgress DB so running in my own TZ. The remote host happens to have its system time set to UTC:
$ date
Mon Oct 7 15:45:00 UTC 2019
$ psql
> select localtimestamp;
2019-10-07 15:45:00.123456
I have a table with an automatically updated date in it (meaning it updates when record is updated).
// my.entity.ts
#UpdateDateColumn({type: 'timestamp', name: 'lastUpdate', default: () => 'LOCALTIMESTAMP' })
lastUpdate: Date;
A row is inserted at 12:00 CEST:
> select "lastUpdate" from myTable;
2019-10-07 10:00:00.000000+00
I would like to get the date out in my timezone (CEST) regardless of the server time, so it should return me 2019-10-07 12:00. I prefer to not hardcode any tricks because it should also work on my CEST machine.
Postgress has all the info:
> show timezone;
UCT
it knows it runs on UTC time
I can tell it in which timezone I want the date
So I would expect it to be easy to convert this to my requested format. However, the following examples I found don't seem to work:
> select ("lastUpdate" at time zone 'CEST') from myTable;
2019-10-07 08:00:00.000000+00
> select timezone('CEST', "lastUpdate") from myTable;
2019-10-07 08:00:00.000000+00
There is one way I can get it right, and thats by specifying the current timezone:
> select ("lastUpdate" at time zone 'UTC' at time zone 'CEST') from myTable;
2019-10-07 12:00:00.000000
However, like I said I don't want to hardcode this (as other DB's run at other TZs) and Postgres knows it's own timezone.
Is there another syntax to do this correctly?
All timestamps in Postgres are stored in UTC regardless of the server configuration. This is important to realize, unlike other databases it does not interpret your input to be in its local time zone. However it will present it back in its time zone.
timestamp stores just the time without a time zone. timestamptz stores UTC plus a time zone.
Demonstrating these together on a Postgres server with its time zone set to UTC...
=> create table demo ( time timestamp, timetz timestamptz );
CREATE TABLE
=> insert into demo values ('2019-10-07 10:00', '2019-10-07 12:00 +0200');
INSERT 0 1
=> select * from demo;
time | timetz
---------------------+------------------------
2019-10-07 10:00:00 | 2019-10-07 10:00:00+00
timestamp ignores the offset and simply stores October 7th, 2019 10:00 with no offset. While timestamptz stores the offset of +0200, but presents the time back to me in its own UTC time zone. They're the same point in time.
You could change the database time zone for your session to CEST. Then Postgres will format timestamptz in CEST.
=> set time zone 'Antarctica/Troll';
=> select * from demo;
time | timetz
---------------------+------------------------
2019-10-07 10:00:00 | 2019-10-07 12:00:00+02
But this is brittle. You have to make sure it happens on every connection. Your application is relying on a specific configuration of your database connection. It's an action-at-a-distance anti-pattern. It's not obvious what's doing the formatting, and if it's removed lots of seemingly unrelated things break.
Instead, you should reformat your times as you like after receiving them from the database. You can do this manually...
=> select timetz at time zone 'CEST' from demo;
timezone
---------------------
2019-10-07 12:00:00
But generally this is something your ORM takes care of for you. I don't know typeorm, but most have a means of translating database types consistently. You should be able to set up typeorm to automatically translate Postgres timestamptz into your local application time zone. Better yet, instead of returning a string it can translate it into a proper Time object which you then have full control over.
select created_at at time zone 'utc' at time zone 'america/los_angeles'
from users;
select ts_tz AT TIME ZONE 'UTC' from test;
I'm struggling to understand how "AT TIME ZONE 'localtime'" exactly work? By playing with it, I found out that it acts exactly as "AT TIME ZONE 'UTC'"... But why? Is "localtime" a synonym of "UTC" in postgres? Or it comes from some setting (environment? connection timezone? although checked both, seems they are not related)...
There's "localtime" function but I think it is not involved here.
Sample SQLs:
# date
Thu Dec 8 12:00:05 AEDT 2016
# SELECT LOCALTIMESTAMP;
----------------------------
2016-12-08 01:13:29.444725
# SELECT LOCALTIMESTAMP AT TIME ZONE 'America/New_York';
-------------------------------
2016-12-08 06:08:31.183103+00
# SELECT LOCALTIMESTAMP AT TIME ZONE'localtime';
------------------------------
2016-12-08 01:09:25.294063+00
# SELECT LOCALTIMESTAMP AT TIME ZONE 'utc';
-------------------------------
2016-12-08 01:09:44.32587+00 -- SAME AS ABOVE
# SET TIME ZONE 'America/New_York';
# SELECT LOCALTIMESTAMP;
----------------------------
2016-12-07 20:13:34.924647
# SELECT LOCALTIMESTAMP AT TIME ZONE 'localtime';
------------------------------
2016-12-07 15:10:08.188197-05
# SELECT LOCALTIMESTAMP AT TIME ZONE 'utc';
------------------------------
2016-12-07 15:10:44.88332-05 -- SAME AS ABOVE
Any hint? Is it documented somewhere?
A timestamp in Postgres does not actually store any timezone information. Rather, this information comes from the timezone which is set by the server. Internally, all timestamp information is recorded in UTC time. So, for example, if you stored timestamp information from a timezone other than UTC, Postgres would first convert that timestamp to UTC before storing it.
From the documentation:
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 your actual question, localtime is just the timezone of the server which is always UTC.
Furthermore, it appears that Postgres' localtime simply wraps the C library function localtime(), which attempts to find the local system time (which is in default UTC time). Again, from the documentation:
If timezone is not specified in postgresql.conf or as a server command-line option, the server attempts to use the value of the TZ environment variable as the default time zone. If TZ is not defined or is not any of the time zone names known to PostgreSQL, the server attempts to determine the operating system's default time zone by checking the behavior of the C library function localtime(). The default time zone is selected as the closest match among PostgreSQL's known time zones. (These rules are also used to choose the default value of log_timezone, if not specified.)
I am struggling in understanding how PostgreSQL is working with TIMESTAMP and TIME ZONE. I have a Debian Server where timezone is set to UTC running PostgreSQL 9.3 where cluster's postgresql.conf file is also set to UTC. My client is PgAdmin and my computer locale is also set to UTC. Therefore, all timezones are equals, there are no offsets and no DST in storage or display.
I have read many posts over the internet and I cannot understand the following output of my queries.
I assume as true the following affirmations:
Default data-type TIMESTAMP is WITHOUT TIME ZONE;
PostgreSQL stores all TIMESTAMP and TIMESTAMPTZ in UTC;
When using TIMESTAMP type, timezone conversion is not performed;
When using TIMESTAMPTZ type timezone conversion is performed;
POSIX and ISO standards define offset in a opposite fashion;
PostgreSQL display in ISO format but abbreviation are POSIX compliant.
First question: are all those statements right?
Then I checked it out, issuing:
SELECT '2000-01-01 00:00:00' AT TIME ZONE 'UTC-1';
-- Result: 2000-01-01 01:00:00
-- UTC --> LT
-- TIMESTAMP
SELECT '2000-01-01 00:00:00'::TIMESTAMP AT TIME ZONE 'UTC-1';
-- Result: 1999-12-31 23:00:00+00
-- LT --> UTC
-- TIMESTAMPTZ
SELECT '2000-01-01 00:00:00'::TIMESTAMPTZ AT TIME ZONE 'UTC-1';
-- Result: 2000-01-01 01:00:00
-- UTC --> LT
-- TIMESTAMP
This is very confusing to me because:
it looks like default data-type infered from string without cast is TIMESTAMPTZ instead of TIMESTAMP;
conversion is performed in different way when using different data-type;
when specifying data-type with casting ::operator it is the opposite type that is retured.
Second question: How must I interpret the result of those three queries?
Bonus question: I have read there that it is better to always store data with TIMESTAMPTZ. Is this a good practice?
Thank you further for your help!
I run a Postgres 8.3 database where times seem to be stored in UTC without time zone.
I am trying to display in local time but not with '+01' suffix :
With select scheduled_start_ts I get :
2014-01-20 05:01:35.663
With select scheduled_start_ts at time zone 'MET' :
2014-01-20 05:01:35.663+01
I would like to get "2014-01-20 06:01:35.663" which is in local time.
The database I am using cannot be modified and I am not allowed to modify how data are stored.
If you want to format times, use the to_char function. See formatting functions in the docs.
regress=> SELECT to_char(
(TIMESTAMP '2014-01-20 05:01:35.663' AT TIME ZONE 'UTC')
AT TIME ZONE 'MET',
'YYYY-MM-DD HH:MI:SS'
);
to_char
---------------------
2014-01-20 06:01:35
(1 row)
The (TIMESTAMP 'xxx' AT TIME ZONE 'UTC') gets me a timestamptz with the correct time, by re-interpreting the TIMESTAMP as being in UTC. The second AT TIME STAMP instead converts the timestamptz into a timestamp in timezone MET. This then gets formatted.
Whatever the SQL standards committe were smoking when they designed this, I never, ever, ever want to be anywhere near it.
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.