Currently my table has stored the time in local time (+11:00 Sydney Australia) and I would like to convert all the values in the time column to UTC time.
The table format looks like:
Time
Suburb
2022-10-01 00:00
Cheltenham
2022-10-31 23:59
Epping
What I am hoping to get is:
Time
Suburb
2022-09-30 14:00
Cheltenham
2022-10-31 14:00
Epping
Is there a way that I can update all the rows in the time column? I have tried using the subquery
UPDATE time_table
SET time = (Select timezone('Australia/Sydney', time) from time_table)
However, it errors with "more than one row returned by a subquery used in expression". I realise that the subquery can only return 1 result, however is there a way where I can update all the rows in the Time column?
A header
Another header
First
row
Second
row
Provided that the data type of the column is timestamp (without time zone), you could
UPDATE tab
SET time = time AT TIME ZONE 'Australia/Sydney' AT TIME ZONE 'UTC';
First, the timestamp is interpreted as Australian time and converted to the corresponding timestamp with time zone, then we get the timestamp that a UTC clock shows at that time.
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 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?
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 have a problem that is
I migrate database table from rails.
In the tables columns timestamps with timezone is also include.
When I insert data into database, timestamp columns save current time as (eg. 2012-08-09 12:00:00 UTC+6:30)
I think it means 2012-08-09 18:30.
but when i retrieve this data from rails 3.2.6 it display as 2012-08-09 5:30
Why it display as 1 hour different from actual time. Is there any idea? please
At a guess, you're storing it with one timezone setting and retrieving it with a different one.
For example, if Rails thinks you're in UTC+6:30 but PostgreSQL thinks you're in UTC+5:30, and if Rails sends dates to Pg timezone qualified but reads them from Pg with the assumption that they're in local time, this would happen. It's safest to make sure your database driver always reads and writes dates timezone-qualified.
Given the one hour gap, I'm wondering if daylight savings is involved, but it could also just be that your timezone is off by one hour.
regress=# create table test ( x timestamp with time zone );
CREATE TABLE
regress=# insert into test (x) values ('2012-08-09 12:00:00 UTC+6:30');
INSERT 0 1
regress=# SET TIMEZONE = '-5:30';
SET
regress=# select * from test;
x
---------------------------
2012-08-10 00:00:00+05:30
(1 row)
regress=# SET TIMEZONE = '-6:30';
SET
regress=# select * from test;
x
---------------------------
2012-08-10 01:00:00+06:30
(1 row)
Alternately, maybe your database is in time zone '-1:00' and your application is stripping off the time zone when it reads the date, so the date appears to be off by one hour. It's hard to say with the available information.
To really help you it would be necessary for you to show:
The code that inserts the date
The INSERT statement that really inserts the date, captured by enabling log_statement = 'all' in postgresql.conf, along with any SET TIMEZONE statements that session ran before the INSERT.
The result of SELECTing that column from the database after a SET TIMEZONE = 'UTC'
and the code that reads the date
the time
2012-08-09 12:00:00 UTC+6:30
is in the timezone UTC+6:30(GMT+6:30) when you save it.
When you retrieve it you get the time in GMT timezone.
Both are same timings as 2012-08-09 5:30 GMT = 12:00:00 GMT+6:30.
EDIT:
This is for #CraigRinger...
Let's say...
UTC is London and UTC + 6:30 is Rangoon so...
6:30 at Rangoon = 12:00 at London
Subtracting 6:30 from both
12:00 at Rangoon = 5:30 at London
12:00 UTC+6:30 = 5:30 UTC
Data stored in UTC+6:30 = Data retrieved in UTC
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.