According to mysqltutorial
The values of the MySQL TIMESTAMP columns depend on connection’s time
zone. When insert values for MySQL TIMESTAMP columns, they are
converted to Universal Coordinated Time (UTC) from connection’s time
zone. When you select the value, the server converts it back from UTC
to the connection’s time zone so you have the same value that you
inserted.
Where does it get this info. from, the time the user sets his OS to or from some other method?
Javascript also has a way to do timezones but is more involved: onlineaspect
To specify connection-specific time you need to perform
SET time_zone = TZ;
Where TZ can be either numerical offset like +11:00 or name of timezone Asia/Vladivostok (for the latter you need to import timezones description. Ask your DBA to do so)
the example there is wrong, i just tested it. it returns the previously inserted timestamp, regardless of the timezone. mysql will always insert the time you specify, without modifying it. if you need timezone adjustment, you have to tell mysql explicit to do so; otherwise all times are assumed to be "local server time".
Related
I am using DATETIME field to store my dates in MySQL. Without any timezone specified directly (there is just a datetime column)
But when timezone was changed on server MySQL updated all datetime columns according to new timezone.
Actually switching to EDT was the reason.
I don't need to recalculate my dates automatically - just want to store specific dates in it.
So even if tz changed manually to UTC from EST date should be same (from characters POV) if it was 2016-01-01 18:55 it should be same in any new tz..
I did not run any scripts\queries to update dates.
So it was performed either by MySQL itself or by server.
Need advice what I need to check to find and disable such feature.
Make sure you are using DATETIME and not TIMESTAMP
[From the MySQL documentation][1]:
MySQL converts TIMESTAMP values from the current time zone to UTC for storage, and back from UTC to the current time zone for retrieval. (This does not occur for other types such as DATETIME.)
You should also review this post (Duplicate):
Will changing a MySQL timezone change values of DateTime fields in a database?
I am sorry for the mess I brought
Just extended my query to grab some old dates - and it looks unchanged
So error defenetly in my code..
Anyway - thanks for your help
I run the following MySQL query:
select unix_timestamp('2011-03-13 02:00:13'), unix_timestamp('2011-03-13 02:20:41'), unix_timestamp('2011-03-13 02:40:10');
And get the following odd result:
1300003200, 1300003200, 1300003200
I think there's some kind of daylight savings time going on here, though it still seems odd that all the values are magically the same.
I'd appreciate suggestions of how to prevent MySQL from doing daylight savings time things here, as well as some explanation as to why all the results are the same.
MySQL's behavior is correct, if your server's time zone "CDT" observes DST and you haven't set your session time zone to something different.
The UNIX_TIMESTAMP() function uses your session's time zone to interepret the value you give it.
The server interprets date as a value in the current time zone and converts it to an internal value in UTC.
...
Note: If you use UNIX_TIMESTAMP() and FROM_UNIXTIME() to convert between TIMESTAMP values and Unix timestamp values, the conversion is lossy because the mapping is not one-to-one in both directions. For example, due to conventions for local time zone changes, it is possible for two UNIX_TIMESTAMP() to map two TIMESTAMP values to the same Unix timestamp value. FROM_UNIXTIME() will map that value back to only one of the original TIMESTAMP values.
— http://dev.mysql.com/doc/refman/5.5/en/date-and-time-functions.html#function_unix-timestamp
The timestamps in question did not exist in your time zone, so the server is giving you the most accurate possible answer... it's the time in UTC that the clock moved forward to, when the time moved forward, less than an hour prior to your datetime literals, which represent "times that never existed on that day" in your time zone.
If those timestamps are intended to be times in your local time zone, then the answer is that those are invalid values, since that time never happened where you are. On the other hand, if those timestamps are actually assumed to already be in UTC, then you're not getting the correct answer from UNIX_TIMESTAMP() on any query, because the time is being converted "from" a time zone it isn't actually expressed in.
If you SET ##TIME_ZONE = 'UTC'; and repeat the queries, you'll see what I mean, since UTC has no DST. This statment only sets your session's time zone, not the whole server.
If running SET ##TIME_ZONE = 'UTC'; gives you an error message such as ERROR 1298 (HY000): Unknown or incorrect time zone: 'UTC', it is likely that you have not populated MySQL with timezone information. As described here you can load this information by using the command:
mysql_tzinfo_to_sql /usr/share/zoneinfo/ | mysql -u root mysql -p
where the path /usr/share/zoneinfo may need to be replaced with a path specific to your system.
I'm working on a shared hosting so I don't have access to mysql configuration files.
The default timezone on that system is 'America/New_York' but I need to use UTC -5:00 for my databases.
Everytime I perform a query the timezone is set to UTC -5:00 like this:
SET time_zone='-5:00';
If I want the current time, SELECT NOW() returns the correct time and date, but when updating a table mysql uses the SYSTEM time and not the set timezone
UPDATE administradores SET ultimo_acceso=NOW() WHERE id=1
Why does those values are different? Shouldn't be the same time in both queries since I'm overriding the timezone?
I also tried with INSERT statement and that works fine.
If the ultimo_acceso field is of type TIMESTAMP, then the value is actually being stored as UTC and then converted back to the current time zone when you select the value back out. So you need to set the time zone again in the select statement.
If you are using a DATETIME data type, then the value you set should be persisted without conversion and you will get back exactly what you store - regardless of the timezone setting at time of select.
See the MySQL docs on this subject.
Note that DATETIME, DATE, and TIME fields will always return the exact time you placed into them, regardless of the value of the time_zone variable.
TIMESTAMP fields will automatically convert their values to the timezone specified by the time_zone variable.
Is there is any possibility in database, What ever time i am given which should store as GMT time stamp. If it so, Please share me.
For PostgreSQL, your table should have a column of type timestamp with time zone (timestamptz for short) like this:
CREATE TABLE tbl (id serial, ts timestamptz);
If what you want to store (let's call it my_ts) is ...
a local timestamp without time zone, i.e. it agrees with the current setting of timezone in your client:
Insert as is, everything is saved as UTC automatically internally:
INSERT INTO tbl (ts) VALUES my_ts'
a timestamp with time zone:
Insert as is, everything is saved as UTC automatically internally:
INSERT INTO tbl (ts) VALUES my_ts;
a timestamp without time zone but from another time zone:
Say, you get timestamp without time zone values from the Olympic Games in London, but your client thinks you are at a different time zone. Transform the timestamp with the AT TIME ZONE construct:
INSERT INTO tbl (ts) VALUES my_ts AT TIME ZONE 'Europe/London';
If you use the time zone name (instead of a time zone abbreviation, BST in this case), DST (daylight saving time) rules are applied automatically. Details in this related question.
More about timestamp handling in PostgreSQL in this related answer.
Now, if you want to display tbl.ts as UTC (~ GMT) timestamp without time zone, regardless of your current time zone, retrieve the values like this:
SELECT ts AT TIME ZONE 'UTC' FROM tbl;
Note that AT TIME ZONE has a different effect when applied to timestamptz than with timestamp! Read the manual carefully.
http://dev.mysql.com/doc/refman/5.5/en/datetime.html
MySQL converts TIMESTAMP values from the current time zone to UTC for
storage, and back from UTC to the current time zone for retrieval.
(This does not occur for other types such as DATETIME.) By default,
the current time zone for each connection is the server's time.
Times in timestamp with time zone (and the old-style timestamp, but you shouldn't generally use that) are always stored in UTC ("GMT") in PostgreSQL. They're converted to and from UTC for display. If you want them to be treated as UTC for input and output:
SET timezone = 'UTC'
in each session, or set the param at the database or user level. Your app must then send all timestamps qualified with a time zone if they're in a TZ other than UTC; you've told the system that "local time" is UTC.
The AT TIME ZONE construct can be useful if you want to explicitly convert timestamps to a time zone other than the default, eg:
regress=# SELECT TIMESTAMP '2012-01-01 00:00:00 UTC' AT TIME ZONE '+08:00';
timezone
------------------------
2012-01-01 16:00:00+08
(1 row)
The keyword you are looking for is UTC instead of GMT ("For most common purposes, UTC is synonymous with GMT, but GMT is no longer precisely defined by the scientific community.", wikipedia).
For MySQL, you can use the CONVERT_TZ() function (please note the warning in the manual about named time zones, it can break your queries if it's not properly set up).
Just a word of caution: there is no 100% reliable way to work with timezone conversion between MySQL and your application (see my blog post about mysql time zone conversions to learn in detail about why this is). It's better to pass your datetime strings to MySQL in UTC directly (e.g. by doing the conversion in the application itself). You almost always end up storing datetimes in a DATETIME field using UTC formatted date strings if you need reliability.
Say I have multiple servers in multiple locations and I want to use MySQL's datetime type for the field date and I always want to have the field date have the UTC timestamp so I would execute a UTC_TIMESTAMP() when I add it to the database. Now say I want to have MySQL output the UNIX TIMESTAMP for it.
When I do this on Server A I get the string "2009-06-17 12:00:00" doing the UNIX_TIMESTAMP(STRING) on it gives me the number 1245240000 back. Which is 2009-06-17 12:00:00 in UTC time. Now I do the same thing on Server B.
I get the same string back since its the UTC string but when executing UNIX_TIMESTAMP(STRING) again I get back the wrong number back 1245232800 which is the UTC +2 time. How do I get around this? Should I do the convertion from string to timestamp on the PHP side?
G'day,
I'll ask the obvious here, did you check the date and time on both machines?
Edit: ... and the MySQL timezone was the same on both machines?
Update: Ok. The problem is in the fact that the timestamp string being passed into UNIX_TIMESTAMP is interpreted to be a value in the current timezone which is then converted back to UTC so, because you're in MEZ, two hours is subtracted to return it back to UTC so 7200 is subtracted from your timestamp when it is converted back to a Unix timestring.
Hence, the variation you see when using UNIX_TIMESTAMP() to convert is back to a Unix Epoch timestring.
BTW Shouldn't you be using a TIMESTAMP type for storing off your UTC_TIMESTAMPs instead of DATETIME type?
Update: Decoupling presentation time from stored time is definitely the way to go. You can then reuse the same data all around the world and only have to convert to and from local time when you are presenting the data to a user.
If you don't do this then you are going to have to store off the timezone when the timestamp was made and then go into all sorts of complicated permutations of having to work out if
the local timezone was in daylight saving time when it was stored,
what the difference is between the timezone at the time that the data was stored and the timezone where the data is to be presented.
Leaving it all storeed as UTC gets rid of that.
Most users won't be that happy if they have to work out the local time themselves based on the UTC time returned so systems usually convert to current local time for the user.
This is of course if the user wants the data expressed in local time which is usually the case. The only widely used system I can think of, off the top of my head, that stores and presents its data in UTC is system for air traffic control and flight plan management which are always kept in UTC (or ZULU time to be more precise).
HTH
cheers,
Have you tried doing this?
Execute this instructions together.
SET time_zone = 'UTC';
SELECT FROM_UNIXTIME(0), UNIX_TIMESTAMP('2009-06-17 12:00:00');
// 1970-01-01 00:00:00 1245240000
They only affect the client session, not the server configuration.