In PostgreSQL, how do I get the epoch (UTC time) of a table date field whose time zone is assumed to be GMT and whose hours, min, seconds value is assumed to be '00:00:00'?
e.g. mytable.DT_GMT has values like '2018-10-16'.
Here's what I've tried so far. Instead of DT_GMT, I've just used '2018-10-16'. I'll replace it with the table field once I have some thing that works.
postgres=> select extract(epoch from TIMESTAMP WITH TIME ZONE concat('2018-10-16',' 00:00:00.00-00') );
ERROR: syntax error at or near "concat"
LINE 1: ...elect extract(epoch from TIMESTAMP WITH TIME ZONE concat('20...
Trying something related:
postgres=> SELECT TIMESTAMP ('2018-10-16' || ' 00:00:00.00') AT TIME ZONE 'GMT';
ERROR: syntax error at or near "'2018-10-16'"
LINE 1: SELECT TIMESTAMP ('2018-10-16' || ' 20:38:40') AT TIME ZONE ...
Note that the hours...sec is necessary because without it those values are not what's required.
postgres=> SELECT TIMESTAMP '2018-10-16' AT TIME ZONE 'GMT';
timezone
------------------------
2018-10-15 17:00:00-07
(1 row)
Instead of a string concatenation, you add them as date and time with time zone.
test=> select extract(epoch from date '2018-10-16' + time with time zone '00:00:00.00-00');
date_part
------------
1539648000
(1 row)
If you're only adding '00:00:00' to make the time zones work, you don't need it with a date.
test=> select date_part('epoch', date '2018-10-16');
date_part
------------
1539648000
$ date --date '#1539648000' --utc
Tue Oct 16 00:00:00 UTC 2018
This is a good reason to store dates and times as their proper type, especially in Postgres which cares a lot about types, rather than as text.
Related
Using PostgreSQL and trying to query a table that contains a UTC column. The UTC column is a column without the timezone as I understand it from the developer. Example in my DB for a record is (2021-08-26 13:59:26.867578). And I have to search for records that are between yesterday's date and today's date. When I tried the SQL statement below I get this error:
[42883] ERROR: operator does not exist: timestamp without time zone - integer Hint: No operator matches the given name and argument types. You might need to add explicit type casts. Position: 63
Here is my SQL statement for PostgreSQL:
SELECT omd.*
FROM "OCRMetaDatas" omd
WHERE (omd."ScannedAt")-5 BETWEEN Now()-1 and now()
ORDER BY omd."ScannedAt" desc;
Any help/direction would be appreciated. Thanks.
You can't operate integer with datetimes. Here you are trying to do that twice:
(omd."ScannedAt")-5
and
Now()-1
You should use INTERVAL with datetime there, such as:
SELECT omd.*
FROM "OCRMetaDatas" omd
WHERE (omd."ScannedAt")- '5 days'::INTERVAL BETWEEN Now()- '1 day'::INTERVAL and now()
ORDER BY omd."ScannedAt" desc;
As illustration of how to use at time zone:
--My TimeZone
show TimeZone;
TimeZone
------------
US/Pacific
select '2021-08-26 13:59:26.867578'::timestamp;
timestamp
----------------------------
2021-08-26 13:59:26.867578
select '2021-08-26 13:59:26.867578'::timestamp at time zone 'UTC';
timezone
-------------------------------
2021-08-26 06:59:26.867578-07
select now();
now
-------------------------------
2021-08-26 09:23:57.818477-07
at time zone will normalize the timestamps to the same time zone.
I am on PostgreSQL v11.10, and have the TimeZone set to UTC.
When I say select '2021-02-16 17:45+00' at time zone 'America/New_York';, I get 2021-02-16 12:45:00, which is correct and expected.
However, when I say select '2021-02-16 17:45' at time zone 'America/New_York';, I get the same result.
It seems like both strings are coerced to timestamp with time zone, which seems a bit counterintuitive to me in the case of the latter one. Why does PostgreSQL behave like that? Is it documented in the manual (I looked at the following places: AT TIME ZONE, then Date/Time Types and also Date/Time Input Interpretation and Handling of Invalid or Ambiguous Timestamps, all to no avail).
Because your TimeZone is set to UTC, any timestamp without a specified timezone will be interpreted as local to the UTC timezone. Since you as asking for a timestamp to be interpreted as America/New_York, Postgres will first interpret the timestamp as a UTC timestamp, then do the math to convert it to America/New_York.
Note that if you actually look at the types being sent to Postgres, it is not coercing into timestamp with timezone unless you specify it:
edb=# select pg_typeof('2021-02-16 17:45' at time zone 'America/New_York');
pg_typeof
-----------------------------
timestamp without time zone
(1 row)
edb=# select pg_typeof('2021-02-16 17:45+00' at time zone 'America/New_York');
pg_typeof
-----------------------------
timestamp without time zone
(1 row)
edb=# select pg_typeof('2021-02-16 17:45+00'::timestamptz at time zone 'America/New_York');
pg_typeof
-----------------------------
timestamp without time zone
(1 row)
edb=# select pg_typeof('2021-02-16 17:45+00'::timestamptz);
pg_typeof
--------------------------
timestamp with time zone
(1 row)
edb=# select pg_typeof('2021-02-16 17:45+00'::timestamp);
pg_typeof
-----------------------------
timestamp without time zone
(1 row)
I have a simple postgresql table with the following data:
create table ti (
l text,
t timestamp without time zone
);
insert into ti(l, t) values ('now', now());
I do a select using at time zone, I expect UTC + 5.30 hours
select now(), t, t at time zone 'Asia/Kolkata' from ti;
But this is what I get:
now| t| timezone
2019-06-06T12:11:42.576388Z| 2019-06-06T11:50:48.178689Z| 2019-06-06T06:20:48.178689Z
It subtracted 5.30 hours instead of adding them.
Sqlfiddle here
now() returns a timestamp with time zone. The time zone info will be stripped off when it is cast to a timestamp without time zone when it is saved in your table, but the actual value saved in there will depend on the session time zone.
You can see this behavior pretty easily:
postgres=# begin;
BEGIN
postgres=# set time zone utc;
SET
postgres=# insert into test select now();
INSERT 0 1
postgres=# set time zone 'US/Eastern';
SET
postgres=# insert into test select now();
INSERT 0 1
postgres=# select * from test;
a
----------------------------
2019-06-06 12:46:10.475424
2019-06-06 08:46:10.475424
(2 rows)
A little more explanation after your comment. I think the issue you are having is with converting between timestamp and timestamptz. Timestamps are much less confusing if you stick with just timestamptz. Let's remove now() from the discussion, since that adds an additional layer of complexity because converting from the result of now() to a timestamp without time zone depends on the session time zone.
select '2019-06-06 12:00:00UTC'::timestamp with time zone,
('2019-06-06 12:00:00UTC'::timestamp with time zone) at time zone 'Asia/Kolkata';
timestamptz | timezone
------------------------+---------------------
2019-06-06 12:00:00+00 | 2019-06-06 17:30:00
I believe this is what you expect? We convert from a timestamp with time zone to a timestamp without time zone at a specific time zone.
What you are doing is similar to this, though:
select '2019-06-06 12:00:00UTC'::timestamp with time zone,
(('2019-06-06 12:00:00UTC'::timestamp with time zone)::timestamp without time zone) at time zone 'Asia/Kolkata';
timestamptz | timezone
------------------------+------------------------
2019-06-06 12:00:00+00 | 2019-06-06 06:30:00+00
(1 row)
I think you will find this much less confusing if you can store timestamp with time zone instead of timestamp without time zone.
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 store timestamps with time zone in my postgres database. The server time zone is UTC. All the timestamptzs are stored as UTC datetimes.
Now, I'd like to retrieve those timestamps, but for a specific time zone (e.g. US/Pacific). Because of daylight savings time, the correct time zone is sometimes PDT and sometimes PST. So I can't just run a query like select t at time zone 'pdt' because this will be wrong for the pst dates.
Is there a way to pull the dates from the database in the correct time zone?
According to the documentation, together with TIME ZONE code you can also specify locales. For your case you can use something like that:
ds=# SELECT current_setting('TIMEZONE');
current_setting
-----------------
UTC
(1 row)
ds=# SELECT now();
now
-------------------------------
2015-11-05 00:35:03.126317+00
(1 row)
pm7=# SELECT now() AT TIME ZONE 'America/Los_Angeles';
timezone
----------------------------
2015-11-04 16:35:06.344367
(1 row)