select current_time at time zone 'GMT-2'
returns
"11:54:40.22045+02"
but correct local time in Windows is one hour different:
12:54
How to get correct local time ?
Using
"PostgreSQL 9.6.0, compiled by Visual C++ build 1800, 32-bit"
with standard postgresql.conf file in Windows 10
Same issue occurs also in ealier Postgres and in earlier windows.
Server time in Windows is correct.
Daylight saving time was changed by one hour a week ago.
Maybe postgres didnt recognized it.
Don't use time with time zone, it is a useless data type.
See the documentation:
The type time with time zone is defined by the SQL standard, but the
definition exhibits properties which lead to questionable usefulness.
In most cases, a combination of date, time, timestamp without time zone,
and timestamp with time zone should provide a complete range of date/time
functionality required by any application.
Use localtime to get the current time at your current session time zone (defined by the TimeZone parameter).
Related
I'm using SAP SQL Anywhere 17 and have a timestamp (without time zone) which I know is UTC, and I know that my client's browser reports a time zone of "Europe/Berlin".
Is there an easy way to convert the UTC timestamp to a local timestamp of this time zone using SQL? Let's assume that I have already created the timezone with
CREATE TIME ZONE "Europe/Berlin" OFFSET '01:00' DST OFFSET '01:00' DST STARTING 'Mar/last Sun' AT '02:00' DST ENDING 'Oct/last Sun' AT '02:00';
I guess it is possible to do it manually using the SYSTIMEZONE view, but it is some hours of hard work to handle all the special cases! Maybe someone has done it already, or Anywhere provides a system function which I have overlooked in the docs.
Note that the problem is to find out whether DST is active at an arbitrary UTC timestamp. Using just the current offset will give wrong results if the timestamp is, for example, 6 months in the future!
When the timezone is activated on your server you have a connection property called TimeZoneAdjustment that returns the number of minutes relative to UTC. For Europe/Berlin this is "60" (during winter time/standard time).
You could add that offset manually using the DATEADD function:
SELECT CURRENT UTC TIMESTAMP AS my_utc_timestamp,
DATEADD(minute, CONNECTION_PROPERTY('TimeZoneAdjustment'), my_utc_timestamp) AS localtime
Newer versions of SQL Anywhere 17 have a new function TOLOCALDATE that automatically applies the current connection's offset to an UTC timestamp (although I couldn't test that function cause my version is to old).
I'm struggling to deal with time zone and daylight saving when querying SAP HANA. The datetime stamp is in the form of NVARCHAR, eg 20210304132500 YYYYMMDDHHMISS in UTC, which means local time is 14:25:00(GMT +01:00) but my query returns 13:25:00 (UTC). How do I edit my results to match local time? Sample query below if that helps.
SELECT DATE_TIME,LOCATION,PART_NUMB
FROM "PUBLIC"."internal.sap.datamodel::ACTIVITY"
WHERE SUBSTRING(DATE_TIME,9,2) IN ('08','11')`
The desired result is local date_time in any format.
HANA comes with timezone conversion functions (UTCTOLOCAL) that can perform the necessary calculations.
These functions require that the data/time input is in either SQL date/time format or that it can be converted to that. They also require that the timezone data has been set up and maintained in the HANA DB. This is the actual information about which timezone has which offsets and daylight saving begin and end times.
For your example, it may make sense to expose the DATE_TIME as a type converted field DATE_TIME_UTC that is already in sql-date time:
to_seconddate (DATE_TIME, 'YYYYMMDDHHMISS') as DATE_TIME_UTC
With this conversion done, you can convert the timezone like this:
UTCTOLOCAL (DATE_TIME_UTC, 'Berlin', 'platform') as LOCAL_DATE_TIME
Note, that the target time zone name may be something like "GMT+1" but this is really just a name and not a calculation instruction. If "GMT+1" is not found in the list of timezone conversions, HANA won't just add an hour - it won't perform the calculation.
With this data type and timezone conversion done, you could have a WHERE clause like this:
WHERE
HOUR(LOCAL_DATE_TIME) IN (8, 11)
This order of transformations (data type -> time zone -> hour component) is of course rather expensive. It may be worthwhile to check whether the resulting query performance is satisfactory on realistic data volume.
Also important to note is that time zone conversion only works on complete date-time information, not just the time. That is to say, if the date is unknown, it cannot be determined which offset rule between two time zone applies. So, simply separating the hours and date components won't help in this case.
Finally, I've written quite a bit about handling date, time, and time zones in HANA, you may want to have a look at that:
The time is now, isn’t it?
Trouble with time?
You got the time?
In PostgreSQL, the data types timestamp and timestamp with timezone both use 8 bytes.
My questions are:
What format is used to store date & time in a timestamp?
How is the time zone information stored in the timestamp with timezone
type, and how is it parsed later when reading the type?
This is just a misunderstanding stemming from the somewhat misleading type name. The time zone itself is not stored at all. It just acts as offset to compute a UTC timestamp (input), which is actually stored. Or as decorator in the display of a timestamp according to the current or given time zone (output). That's all according to the SQL standard.
Just the point in time is stored, no zone information. That's why 64 bit of information is enough. The timestamp is displayed to the client according to the current time zone setting of the session.
Details:
Ignoring time zones altogether in Rails and PostgreSQL
Also, since Jon mentioned it, time with time zone is defined in the SQL standard and thus implemented in Postgres, but its use is discouraged:
time with time zone is defined by the SQL standard, but the definition
exhibits properties which lead to questionable usefulness.
It's an inherently ambiguous type that cannot deal with DST properly.
Looking at the documentation:
Timestamps are stored either as integers, or (deprecated) floating point numbers
I don't believe timestamp with timezone could be correctly encoded within 8 bytes if it actually stored a time zone. Just the timestamp requires 64 bits, as log2(298989 * 365 * 24 * 60 * 60 * 1000000) is greater than 63. Note that time with time zone requires 12 bytes, with the same precision but a range of a single day.
See Erwin's answer to explain how it actually manages to be stored in 8 bytes - it should be called "timestamp without a time zone, but stored in UTC and converted into the local time zone for display". Ick.
I have a TIMESTAMP field in an hsqldb table that I want to set to "2015-02-11 16:02:01.488 America/Los_Angeles", but the insert fails even if I set the column to TIMESTAMP WITH TIMEZONE, the reason being hsqldb seems to support '2008-08-08 20:08:08-8:00' format but not spelled out like America/Los_Angeles. Is there way to make the insert accept America/Los_Angeles type zones ?
Sorry, but hsqldb doesn't support working with IANA/Olson time zones directly. You are correct that TIMESTAMP WITH TIMEZONE only supports a time zone offset. You can review the hsqldb docs for confirmation.
Many databases do not support named time zone. Oracle and Postgres support them, but most others do not.
Consider also that while a named time zone can usually determine the offset, there are still cases of ambiguity around the fall-back daylight saving time transition. In other words, if you had "2015-11-01 01:30:00 America/Los_Angeles", you could not deterministically tell whether it was Pacific Daylight Time (UTC-07:00) or Pacific Standard Time (UTC-08:00). This is why usually just the offset is stored.
The converse is also true though. If you only store "-08:00" then you can't deterministically know that it came from "America/Los_Angeles".
Here's a general guideline that will help:
If the local time is unimportant, then just store a TIMESTAMP based on UTC.
If the local time is important, but the value will never be modified, then store a TIMESTAMP WITH TIMEZONE, using the local time and it's associated time zone offset.
If the local time is important AND the value can be modified, then store a TIMESTAMP WITH TIMEZONE in one column, and the time zone name (ie. "America/Los_Angeles") in a second VARCHAR column, or elsewhere in your database. During an edit operation, use the time zone name to calculate the offset of the new value. It might be the same, or it may be different.
See also DateTime vs DateTimeOffset, which presents a similar argument for .Net and/or SQL Server.
Q1: I want to convert a unix timestamp (INT) to monetdb timestamp ('YYYY-MM-DD HH:MM:SS') format
but it is giving me the GMT time not my actual time.
When I do
select (epoch(cast(current_timestamp as timestamp))-epoch(timestamp '2013-04-25 11:49:00'))
where 2013-04-25 11:49:00 is my systems current time it gives the same difference
I tried using
set time zone interval '05:30' HOUR TO MINUTE;
but it did not change the result
How can I solve this problem??
Example Problem:
I wanted to convert unix timestamp 1366869289 which should be around "2013-04-25 11:25:00" but monetdb gives "2013-04-25 05:55:00"
Knowing nothing about MonetDB, but a lot about timezones, I decided to look in their documentation to see what kind of datatypes are supported and how conversions are handled.
I found this page on Temporal data types. Based on that, I can conclude that a timestamp in MonetDB is always intended to reference UTC/GMT time - which is consistent with other systems.
In order to get a value that is for a particular time zone, they offer the following example:
SET TIME ZONE INTERVAL '1' HOUR TO MINUTE
I assume this means to set the database to offset all times by 1 hour, effectively placing the values all in UTC+01:00, such as is the offset for British Summer Time.
The page also goes on to point out the problems that can arise with using just and offset to adjust time values (see TimeZone != Offset in the TimeZone tag wiki). It also offers a list of various named time zones. But it does not show how to set a time zone to one of the named values. Also, their list appears to be proprietary, and incomplete. While at first glance they appear to have similarities to the IANA/Olson time zone database - the identifiers they specify are not valid TZDB names.
There are some other functions listed on this page, without much explanation. One that looks promising for your needs is LOCALTIMESTAMP. Perhaps this will take the local time zone into account, which appears to be what you were looking for.
I could not find any additional details specific to MonetDB date/time/timezone handling. The documentation appears to be fairly incomplete. You might want to reach out to their mailing list.