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
Related
I have data in GMT timezone. I want to convert and display them in 'America/New_York'.
This is the code I use:
(d.start_time) AT TIME ZONE 'America/New_York'
It returns let's say 2021-10-25T09:30:00.000Z.
9:30 is the correct time. But why is it a UTC time zone timestamp instead of 'America/New_York'?
I tried various variations of with/without time zone and ::timestamp/::timestamptz but I probably doesn't understand something very basic in here...
What should I do differently so that it's valid 9:30am timestamp in 'America/New_York' timezone?
The result is correct: 2021-10-25T09:30:00.000 is a timestamp without time zone, and it is not a UTC timestamp, but local time in New York City.
If you want the timestamp to be displayed with the time zone offset of New York City, you have to do something different:
SET timezone = 'America/New_York';
SELECT current_timestamp;
current_timestamp
═══════════════════════════════
2021-10-11 12:45:49.881037-04
(1 row)
Then PostgreSQL will display timestamp with time zone values with the offset you want.
I just started with PostgreSQL. Since we use a lot of Unixtimestamps I figured it would be best to just try a little example. So I made a table test with a field ID and a field timestamp of type timestamp without time zone using phpPgAdmin. There is valid data.
Now I just wanted to retrieve the data using a Unixtimestamp. And I run into really odd behavior.
I made this little test which selects data by just converting the first best timestamp into a unixtimestamp and back into a timestamp:
This will return the timestamp in the raw and unix value for the first entry
SELECT timestamp, extract(epoch FROM timestamp)
FROM test
WHERE id IN (SELECT id FROM test LIMIT 1);
Ok, that worked as intended.
This does only convert therefore it should return one entry
SELECT timestamp, extract(epoch FROM timestamp)
FROM test
WHERE timestamp IN (SELECT TO_TIMESTAMP(extract(epoch FROM timestamp))
FROM test LIMIT 1);
Nothing is returned!
I just can't wrap my head around this behavior. If I convert a timestamp into something else and then convert it back it should be the same timestamp, right?
I just want a way to cast timestamps into unixtime and back without the chance that information is lost.
Please note: this is just a test! I do not want to use this code. I just want to check if the SQL code behaves as expected!
Also, I can not do anything about the unixtimestamps! I just want a way to cast them properly!
The difference of not using timestamp type without time zone vs with:
select '09/12/2020 11:16 PDT'::timestamp, to_timestamp(extract(epoch from '09/12/2020 11:16 PDT'::timestamp));
timestamp | to_timestamp
---------------------+-------------------------
09/12/2020 11:16:00 | 09/12/2020 04:16:00 PDT
select '09/12/2020 11:16 PDT'::timestamptz, to_timestamp(extract(epoch from '09/12/2020 11:16 PDT'::timestamptz));
timestamptz | to_timestamp
-------------------------+-------------------------
09/12/2020 11:16:00 PDT | 09/12/2020 11:16:00 PDT
UPDATE. For more detail see. the important part is:
In a literal that has been determined to be 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.
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).
This means:
select '09/12/2020 11:16 PDT'::timestamp;
timestamp
---------------------
09/12/2020 11:16:00
select '09/12/2020 11:16'::timestamp at time zone 'UTC';
timezone
-------------------------
09/12/2020 04:16:00 PDT
select '09/12/2020 11:16 PDT'::timestamp at time zone 'UTC';
timezone
-------------------------
09/12/2020 04:16:00 PDT
select '09/12/2020 11:16 PDT'::timestamptz;
timestamptz
-------------------------
09/12/2020 11:16:00 PDT
select '09/12/2020 11:16 PDT '::timestamptz at time zone 'UTC';
timezone
---------------------
09/12/2020 18:16:00
So in the first case the time zone is ignored and the time is taken to be 09/12/2020 11:16 . In the second and third cases the timestamp is taken as being at UTC and the displayed value is rotated to my time zone PDT.In the third case I'm using timestamptz so the timestamp is correctly tagged with the time zone. This means when I ask to display at UTC it does the correct thing.
As documented in the manual to_timestamp() returns a timestamp WITH time zone, so obviously the comparison with a timestamp WITHOUT time zone won't work.
You will need to convert the result from to_timestamp() back to a timestamp without time zone, by telling Postgres which time zone it should take:
SELECT "timestamp",
extract(epoch FROM "timestamp"),
cast("timestamp" as timestamp with time zone),
TO_TIMESTAMP(extract(epoch FROM "timestamp")) at time zone 'UTC'
FROM test
where "timestamp" in (select to_timesatmp(extract(epoch FROM "timestamp")) at time zone 'UTC'
from test
limit 1)
Which is essentially the same as:
SELECT "timestamp",
extract(epoch FROM "timestamp"),
cast("timestamp" as timestamp with time zone),
TO_TIMESTAMP(extract(epoch FROM "timestamp")) at time zone 'UTC'
FROM test
where "timestamp" in (select "timestamp"
from test
limit 1)
But the whole converting back and forth between a number and a proper timestamp is useless - and error prone if you mix different data types (as you have just discovered). The best thing is to keep everything as a timestamp or better as a timestamptz.
For a short introduction why timestamptz (with time zone)` is in general a better choice, you might want to read this
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 am getting my data: date and time in UTC, in a csv file format in separate columns. Since I will need to convert this zone to date and time of the place where I live, currently in summer to UTC+2, and maybe some other zones I was wondering what is the best practice to insert data in postgres when we are talking about type of data. Should I place both of my data in a single column or keep them separate as types: date and time, and if not should I use timestamp or timestampz (or something else).
use timestamptz it will store your time stamp in UTC. and will display it to the client according to it's locale.
https://www.postgresql.org/docs/current/static/datatype-datetime.html
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.
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).
updated with another good point from Lukasz, I had to mention:
Also in favor of single column is the fact that if you would store
both date and time in separate columns you would still need to combine
them and convert to timestamp if you wanted to change time zone of
date.
Not doing that would lead to date '2017-12-31' with time '23:01:01' would in other time zone in fact be not only different time, but different date with all YEAR and MONTH and DAY different
another update As per Laurenz notice, don't forget the above docs quote
An input value that has an explicit time zone specified is converted to UTC using the appropriate offset for that time zone. Which means you have to manage the input dates carefully. Eg:
t=# create table t(t timestamptz);
CREATE TABLE
t=# set timezone to 'GMT+5';
SET
t=# insert into t select '2017-01-01 00:00:00';
INSERT 0 1
t=# insert into t select '2017-01-01 00:00:00' at time zone 'UTC';
INSERT 0 1
t=# insert into t select '2017-01-01 00:00:00+02';
INSERT 0 1
t=# select * from t;
t
------------------------
2017-01-01 00:00:00-05
2017-01-01 05:00:00-05
2016-12-31 17:00:00-05
(3 rows)
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.