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.
How do I convert a timestamp that is in UTC to timestamptz?
If my local time zone is GMT-1 and I run:
select '2017-01-01 00:00:00'::timestamptz
I get:
2017-01-01 00:00:00-01
but I want:
2017-01-01 01:00:00-01
Better:
SELECT timestamp '2017-01-01 00:00:00' AT TIME ZONE 'UTC';
No additional cast after the AT TIME ZONE construct. It returns timestamp with time zone (= timestamptz) for timestamp without time zone (= timestamp) input and vice versa.
For the given example, the shortest, most efficient way to provide a timestamp constant is timestamp '2017-01-01'. Or use a cast, almost as good: '2017-01-01'::timestamp. The time component 00:00:00 is assumed when missing.
There is no such thing as a "timestamp that is in UTC". A timestamp carries no time zone information. Only you know that it's supposed to be located in the UTC time zone.
The type name "timestamp with time zone" is a bit misleading. timestamptz does not carry any time zone information, either. The given time zone name, abbreviation or offset is used to compute the corresponding UTC time. Text output (display) is adapted to the current time zone setting of your session. Only the bare value of the corresponding UTC time is stored. The time zone itself is never stored. If you need it, store it additionally in another column. In your particular case, UTC happens to be the time zone used for input as well.
Detailed explanation:
Time zone storage in data type "timestamp with time zone"
Ignoring time zones altogether in Rails and PostgreSQL
Solution: select ('2017-01-01 00:00:00' at time zone 'utc')::timestamptz
I have date and time fields in my table. Both are set in local server time.
Is it possible to cast both fields as a single UTC ISO timestamp?
Just add the two:
SELECT date_col + time_col AS timestamp_col
The type timestamp [without time zone] is stored as UTC timestamp internally anyway. Only the display is adjusted to the time zone setting of your session. If you need to display the timestamp as UTC timestamp, use the AT TIME ZONE construct:
SELECT timestamp_col AT TIME ZONE 'UTC';
Note that this returns a timestamp with time zone when applied to a timestamp.
Ample details:
Ignoring timezones altogether in Rails and PostgreSQL
For example, to display the timestamp as timestamptz in Moscow:
SELECT (date_col + time_col) AT TIME ZONE 'Europe/Moscow' AS tstz_col
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.