I uploaded csv data into table in postgres. One of the columns is a character varying column with an epoch filling. The data going in is as following:
Example record: 1507656308.
The epoch character varying column is transformed to a timestamp column as follows:
select
TIMESTAMP WITH TIME ZONE 'epoch' + timestamp::integer * INTERVAL '1 second' as timestamp
from
table
The result appeared good and I continued with it. I live in the Netherlands and here we have the winter-summertime change twice a year. Apparently my data does not differentiate.
I tried to figure out my current timezone. Which I did like this:
SELECT EXTRACT(TIMEZONE FROM timestamp) FROM table;
Resulting in:
3,600.0000
When I try to figure out my general time zone I get this:
show timezone
= Europe/Berlin
How do I get my timestamps to recognize the summer vs wintertime? Or what did I do wrong?
Of all the creative ways to convert an epoch value (why is it stored as string?) to a timestamp with time zone, this is one of the more interesting one.
The simple and boring way is
SET timezone = 'Europe/Berlin';
SELECT to_timestamp(1507656308);
to_timestamp
------------------------
2017-10-10 19:25:08+02
(1 row)
The time zone offset for that is two hours, because on October 10, daylight savings time was in effect (Central European Summer Time).
Indeed:
SELECT extract(timezone FROM to_timestamp(1507656308));
date_part
-----------
7200
(1 row)
So everything is working as expected, right?
Related
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'm trying to understand how the session time zone works in PostgreSQL.
When I set session time zone to '01:00', returned date is in '-01:00'. Sign is always inverted and I do not understand this behavior.
How can this be explained?
postgres=# set time zone '00:00';
SET
postgres=# select timestamp with time zone '2017-11-29 15:00:00.000000+00';
timestamptz
------------------------
2017-11-29 15:00:00+00
(1 row)
postgres=# set time zone '01:00';
SET
postgres=# select timestamp with time zone '2017-11-29 15:00:00.000000+00';
timestamptz
------------------------
2017-11-29 14:00:00-01
(1 row)
postgres=# set time zone '-01:00';
SET
postgres=# select timestamp with time zone '2017-11-29 15:00:00.000000+00';
timestamptz
------------------------
2017-11-29 16:00:00+01
(1 row)
example, here
ts is time (text) - just time as we say it, :
not_aware the time if we don't know its timezone (local to the saying person)
aware the time, but knowing the timezone of it(if server time zone is UTC, then of utc zone)
, so:
s=# with s(city,tz) as (values('Moscow','UTC+3'),('New York','UTC-5'))
, ts as (select '2017-01-01 00:00:00'::text ts)
select *,ts::timestamp at time zone tz not_aware, ts::timestamptz at time zone tz aware
from s
join ts on true;
city | tz | ts | not_aware | aware
----------+-------+---------------------+------------------------+---------------------
Moscow | UTC+3 | 2017-01-01 00:00:00 | 2017-01-01 03:00:00+00 | 2016-12-31 21:00:00
New York | UTC-5 | 2017-01-01 00:00:00 | 2016-12-31 19:00:00+00 | 2017-01-01 05:00:00
(2 rows)
lets say you you come from Lodon and have have watches that show UTC0 time
- local for London (this is your server with timezone UTC0). Now are fly to Moscow, looking at the Kremlin Clock and you see the ts, midnight. Your watches are aware of time difference and they show you that to Ney Year is in three hours (this is timestamptz - aware column). This is why UTC+3 requires to minus the time. Because for your server Moscow time is in future, thus when you see local 2017, for server it is still 2016 and gonna be like it for +3 hours...
Now the behaviour that you expected (not_aware column) is more tricky. The server runs at UTC0, but has to pretend it know nothing about the "real time". As timestamp without time zone is such type. So it behaves as if you were watching new year celebration on Red Square on TV and would just scroll the bar to adjust your watches to Kremlin Clock, so in fact the time you see is your London time +3 (not_aware) column.
I came across this while looking for answers to other questions.
In case you never figured it out:
I think this is a quirk of the timezone parsing code trying to follow POSIX syntax, as noted above. You get the same behavior by e.g. SET TIME ZONE 'CET1:00'; or SET TIME ZONE 'CET1'.
I think the "actual" SQL way of saying what you were trying to say is SET TIME ZONE 1.
You probably don't want to have this be set as your timezone anyhow because it doesn't track DST changes. You probably want to choose a timezone by name from the tz database, for example America/New_York or (going with the GMT+1 example) Europe/Madrid.
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)
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.