In a table all the records are stored in GMT time. But through my application i want to display only those records which falls into timezone UTC. i.e., in a web page i want to display only records that comes under UTC time zone.
Converting from GMT to UTC. Or Query the database to get all the records of UTC timezone.
I really appreciate an early reply.
I am using oracle database and application in PHP.
From Greenwich Mean Time on Wikipedia:
It [GMT] is arguably the same as Coordinated Universal Time (UTC).
Regarding converting, you can add/remove intervals, but in so far as I'm aware, Oracle supports timestamps with/without time zones:
select now() at time zone 'UTC' as utc,
now() at time zone 'EST' as est,
now() at time zone 'Europe/London' as london;
The last example, if it works, would allow you to not worry about daylight savings and so forth.
I'll assume that your times are stored as DATE values, that all the values are stored as UTC times, and that the timezone you're interested in is constant. To convert from UTC to a given timezone you add the timezone's offset. In this case, since the timezone of interest has a negative offset you need to add in the same negative number. Thus, the following might be useful:
SELECT DATE_FIELD + INTERVAL '-5' HOUR
FROM SOME_TABLE
WHERE <whatever>
FWIW, there are some places where the conversion to local time uses a non-whole-hour offset - for example, Adelaide, Australia uses a +9.5 hour offset from GMT, and Kathmandu, Nepal uses +5.75 hours.
Share and enjoy.
EDIT: Given the data as you've described it, your best bet is probably to simply add in the session time zone, as follows:
SELECT your_gmt_timestamp_field AT TIME ZONE SESSIONTIMEZONE
FROM your_table
Give this a try and see if it helps.
Related
Right now my Laravel application save() any items into the database base on this timestamp. America/New_York because I configured it as 'timezone' => 'America/New_York', in config/app.php.
Goal
I wish to overwrite timestamp based on other tz instead, ex. America/Chicago
How do I do that?
You don't need too
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.)
see https://dev.mysql.com/doc/refman/5.7/en/datetime.html
So when you change the server to another timezone all timestamps will get the new time zone
setting the time zone goe like
SET GLOBAL time_zone = 'America/Chicago';
You don't have to do crazy stuff... What you have to do is:
Store the time in a known timezone and never change that timezone again, it would be awesome if you use UTC as a default timezone.
When you want to "convert" a timezone, you just $model->created_at (or anything that is a Carbon object) and do $model->created_at->setTimezone('America/Chicago'); (for example).
The main idea is that when you already have a Carbon instance with a timestamp, you just change the timezone with setTimezone to the new one you want and it will return a new Carbon instance with that timezone...
Have a look at this SO topic.
Also, remember that timestamp is just an integer representing how many seconds have passed since 1970-01-01 00:00:01 (UTC), so if you say "give me a timestamp of a specific date and time on specific timezone" the timestamp will be always the same even if you change the timezone each time... that is the main idea of the timestamp...
If I say "What timestamp is for 1970-01-01 00:00:10?", if you are on UTC you would get 10, because 10 seconds passed since that specific datetime, if you are on UTC+1, it would still be 10 seconds, but you will display 1970-01-01 00:01:10, because you are 1 hour ahead of UTC, if you are on UTC-1 it will be 1969-12-31 23:00:10, because you are 1 hour behind UTC, but you know how to do the conversion, that is why the value will be always the same disregarding the timezone, and that is also why it is 1970-01-01 00:00:00 and not any other specific datetime, because if you do not know which is the specific datetime you would not know how to do the conversion.
It is very important that you understand what you are working with, so to help you understand better, have a look at this blog explaining the same thing but in more detail.
The timestamp generated in PHP is in UTC time regardless of your local timezone setting.
You can adjust the timezone of the timestamp before it is displayed in the UI using setTimezone.
Reference:
https://www.php.net/manual/en/function.time.php
https://www.php.net/manual/en/datetime.gettimestamp.php
Today at work we had an argument. You register a user and write in the db the date of creation of the account. The PHP.ini is set to utc and writes the date in UTC. The problem is that when you transform the time for every user (they can set it to the Europe/London and some other countries in Europe. So, the argument was do you get a different time depending on your date-time savings or not and is that a problem for the database?
As long as you are storing in a timestamp column, timezones will not affect your time functions. This is because timestamp stores an absolute time (Epoch time) representing time elapsed since Jan 1 1970 UTC. So, all you will have to do is convert your time to/from Epoch time and your timezone in the browser should be localized. Of course, by storing Epoch time, your times will always be relative to UTC in the database.
I'm using Laravel/PHP/MySQL and storing all dates and times in UTC.
The user can select a timezone (for example Eastern), enter a date and time, and the date and time will be converted to UTC before storing. On retrieval it will be converted to user's selected timezone.
My question is how can you get the average time of day from a series of records taking into account the timezone (preferably in the database query)? The following question addresses average time of day in PHP, but not the timezone issue.
How to calculate average time
Here is what I'm doing:
SEC_TO_TIME( AVG( TIME_TO_SEC( TIME(flights.departed_at) ) ) ) ) AS average_time
This works except for records that span daylight saving/standard time in a region that observes it.
FOR EXAMPLE: You may have a record with the UTC datetime of 2015-08-18 11:00:00 that was entered by a user in EDT at 2015-08-18 07:00:00. Then you have a second record entered with the UTC datetime of 2015-11-10 12:00:00 by a user in EST at 2015-11-10 07:00:00. If you try to calculate the average time of day it should equate to 07:00:00 but instead the result is 07:30:00.
Any ideas how to overcome this? Am I approaching this all wrong?
Thanks in advance.
In short, your code is working correctly. Once the date is in UTC, you'd have to re-calculate whether or not it was entered (1) during daylight savings time, (2) by someone actually observing daylight savings time, and (3) in a place that recognizes daylight savings time.
I can really only think of one way to approach this.
Add some kind of flag when the data is saved to mark the timestamp as DST. You can use this flag to adjust for the hour difference. How you generate this flag is up to you.
If you have all your times stored in Z, and if your MySQL database has the timezones loaded correctly, you can use the zoneinfo timezone name to retrieve your local times. For example,
SELECT CONVERT_TZ('2015-08-01 11:00', 'UTC', 'America/New_York'),
CONVERT_TZ('2015-12-01 12:00', 'UTC', 'America/New_York')
yields
2015-08-01 07:00 2015-12-01 07:00
The point is, the zoneinfo database knows to use daylight saving time or standard time for each datetime value. It doesn't use the current offset, it uses the offset in effect on the date in question.
So, you can retrieve the time of day, in local time, with an expression like this:
TIME(CONVERT_TZ(utc_time_column, 'UTC', 'America/New_York'))
Then, you average those times-of-day in the usual way.
I am using strtotime() to get a timestamp from a date and time string. I will be running strtotime() during the summer (daylight savings) to give me a timestamp of a winter date (non-daylight savings).
In the winter, I will need to convert my timestamp to a readable date using date() -- will it be the same date/time I put into strtotime() during the summer?
On each one of my pages, I am setting my timezone by date_default_timezone_set with my city.
So, running this during the summer (daylight savings):
date_default_timezone_set('America/Los_Angeles');
echo strtotime("Dec 1 2014 8:00 am");
Gives me a certain timestamp 1417449600.
Will running this during the winter (non-daylight savings) return 8:00am as I need it to do?
date_default_timezone_set('America/Los_Angeles');
echo date("g:ia",1417449600);
Yes. If the timezone you set is doesn't explicitly say whether it's standard or daylight-savings time, it automatically determines the state of DST from the time that you give it and the rules for when the timezone switches into and out of DST.
Yes. A UNIX timestamp such as 1417449600 represents a completely, globally, universally unique point in time, independent of fussy timezone notation. There's only one "December 1st 2014 8 am in Los Angeles", which is the same point in time as "December 1st 2014 17:00 CET" and a number of other local notations across the world. The UNIX timestamp 1417449600 expresses that point in time, regardless of whatever your wall clock says exactly.
When you format this unique point in time back to a more human readable format using date(), it figures out what exactly the time must be formatted at based on the set timezone. It won't change based on what the time or DST settings are now.
I'm using the America/New York timezone. In the Fall we "fall back" an hour -- effectively "gaining" one hour at 2am. At the transition point the following happens:
it's 01:59:00 -04:00
then 1 minute later it becomes:
01:00:00 -05:00
So if you simply say "1:30am" it's ambiguous as to whether or not you're referring to the first time 1:30 rolls around or the second. I'm trying to save scheduling data to a MySQL database and can't determine how to save the times properly.
Here's the problem:
"2009-11-01 00:30:00" is stored internally as 2009-11-01 00:30:00 -04:00
"2009-11-01 01:30:00" is stored internally as 2009-11-01 01:30:00 -05:00
This is fine and fairly expected. But how do I save anything to 01:30:00 -04:00? The documentation does not show any support for specifying the offset and, accordingly, when I've tried specifying the offset it's been duly ignored.
The only solutions I've thought of involve setting the server to a timezone that doesn't use daylight savings time and doing the necessary transformations in my scripts (I'm using PHP for this). But that doesn't seem like it should be necessary.
Many thanks for any suggestions.
I've got it figured out for my purposes. I'll summarize what I learned (sorry, these notes are verbose; they're as much for my future referral as anything else).
Contrary to what I said in one of my previous comments, DATETIME and TIMESTAMP fields do behave differently. TIMESTAMP fields (as the docs indicate) take whatever you send them in "YYYY-MM-DD hh:mm:ss" format and convert it from your current timezone to UTC time. The reverse happens transparently whenever you retrieve the data. DATETIME fields do not make this conversion. They take whatever you send them and just store it directly.
Neither the DATETIME nor the TIMESTAMP field types can accurately store data in a timezone that observes DST. If you store "2009-11-01 01:30:00" the fields have no way to distinguish which version of 1:30am you wanted -- the -04:00 or -05:00 version.
Ok, so we must store our data in a non DST timezone (such as UTC). TIMESTAMP fields are unable to handle this data accurately for reasons I'll explain: if your system is set to a DST timezone then what you put into TIMESTAMP may not be what you get back out. Even if you send it data that you've already converted to UTC, it will still assume the data's in your local timezone and do yet another conversion to UTC. This TIMESTAMP-enforced local-to-UTC-back-to-local roundtrip is lossy when your local timezone observes DST (since "2009-11-01 01:30:00" maps to 2 different possible times).
With DATETIME you can store your data in any timezone you want and be confident that you'll get back whatever you send it (you don't get forced into the lossy roundtrip conversions that TIMESTAMP fields foist on you). So the solution is to use a DATETIME field and before saving to the field convert from your system time zone into whatever non-DST zone you want to save it in (I think UTC is probably the best option). This allows you to build the conversion logic into your scripting language so that you can explicitly save the UTC equivalent of "2009-11-01 01:30:00 -04:00" or ""2009-11-01 01:30:00 -05:00".
Another important thing to note is that MySQL's date/time math functions don't work properly around DST boundaries if you store your dates in a DST TZ. So all the more reason to save in UTC.
In a nutshell I now do this:
When retrieving the data from the database:
Explicitly interpret the data from the database as UTC outside of MySQL in order to get an accurate Unix timestamp. I use PHP's strtotime() function or its DateTime class for this. It can not be reliably done inside of MySQL using MySQL's CONVERT_TZ() or UNIX_TIMESTAMP() functions because CONVERT_TZ will only output a 'YYYY-MM-DD hh:mm:ss' value which suffers from ambiguity problems, and UNIX_TIMESTAMP() assumes its input is in the system timezone, not the timezone the data was ACTUALLY stored in (UTC).
When storing the data to the database:
Convert your date to the precise UTC time that you desire outside of MySQL. For example: with PHP's DateTime class you can specify "2009-11-01 1:30:00 EST" distinctly from "2009-11-01 1:30:00 EDT", then convert it to UTC and save the correct UTC time to your DATETIME field.
Phew. Thanks so much for everyone's input and help. Hopefully this saves someone else some headaches down the road.
BTW, I am seeing this on MySQL 5.0.22 and 5.0.27
MySQL's date types are, frankly, broken and cannot store all times correctly unless your system is set to a constant offset timezone, like UTC or GMT-5. (I'm using MySQL 5.0.45)
This is because you can't store any time during the hour before Daylight Saving Time ends. No matter how you input dates, every date function will treat these times as if they are during the hour after the switch.
My system's timezone is America/New_York. Let's try storing 1257051600 (Sun, 01 Nov 2009 06:00:00 +0100).
Here's using the proprietary INTERVAL syntax:
SELECT UNIX_TIMESTAMP('2009-11-01 00:00:00' + INTERVAL 3599 SECOND); # 1257051599
SELECT UNIX_TIMESTAMP('2009-11-01 00:00:00' + INTERVAL 3600 SECOND); # 1257055200
SELECT UNIX_TIMESTAMP('2009-11-01 01:00:00' - INTERVAL 1 SECOND); # 1257051599
SELECT UNIX_TIMESTAMP('2009-11-01 01:00:00' - INTERVAL 0 SECOND); # 1257055200
Even FROM_UNIXTIME() won't return the accurate time.
SELECT UNIX_TIMESTAMP(FROM_UNIXTIME(1257051599)); # 1257051599
SELECT UNIX_TIMESTAMP(FROM_UNIXTIME(1257051600)); # 1257055200
Oddly enough, DATETIME will still store and return (in string form only!) times within the "lost" hour when DST starts (e.g. 2009-03-08 02:59:59). But using these dates in any MySQL function is risky:
SELECT UNIX_TIMESTAMP('2009-03-08 01:59:59'); # 1236495599
SELECT UNIX_TIMESTAMP('2009-03-08 02:00:00'); # 1236495600
# ...
SELECT UNIX_TIMESTAMP('2009-03-08 02:59:59'); # 1236495600
SELECT UNIX_TIMESTAMP('2009-03-08 03:00:00'); # 1236495600
The takeaway: If you need to store and retrieve every time in the year, you have a few undesirable options:
Set system timezone to GMT + some constant offset. E.g. UTC
Store dates as INTs (as Aaron discovered, TIMESTAMP isn't even reliable)
Pretend the DATETIME type has some constant offset timezone. E.g. If you're in America/New_York, convert your date to GMT-5 outside of MySQL, then store as a DATETIME (this turns out to be essential: see Aaron's answer). Then you must take great care using MySQL's date/time functions, because some assume your values are of the system timezone, others (esp. time arithmetic functions) are "timezone agnostic" (they may behave as if the times are UTC).
Aaron and I suspect that auto-generating TIMESTAMP columns are also broken. Both 2009-11-01 01:30 -0400 and 2009-11-01 01:30 -0500 will be stored as the ambiguous 2009-11-01 01:30.
I think micahwittman's link has the best practical solution to these MySQL limitations: Set the session timezone to UTC when you connect:
SET SESSION time_zone = '+0:00'
Then you just send it Unix timestamps and everything should be fine.
But how do I save anything to 01:30:00
-04:00?
You can convert to UTC like:
SELECT CONVERT_TZ('2009-11-29 01:30:00','-04:00','+00:00');
Even better, save the dates as a TIMESTAMP field. That's always stored in UTC, and UTC doesn't know about summer/winter time.
You can convert from UTC to localtime using CONVERT_TZ:
SELECT CONVERT_TZ(UTC_TIMESTAMP(),'+00:00','SYSTEM');
Where '+00:00' is UTC, the from timezone , and 'SYSTEM' is the local timezone of the OS where MySQL runs.
Mysql inherently solves this problem using time_zone_name table from mysql db.
Use CONVERT_TZ while CRUD to update the datetime without worrying about daylight savings time.
SELECT
CONVERT_TZ('2019-04-01 00:00:00','Europe/London','UTC') AS time1,
CONVERT_TZ('2019-03-01 00:00:00','Europe/London','UTC') AS time2;
This thread made me freak since we use TIMESTAMP columns with On UPDATE CURRENT_TIMESTAMP (ie: recordTimestamp timestamp NOT NULL DEFAULT CURRENT_TIMESTAMP ON UPDATE CURRENT_TIMESTAMP) to track changed records and ETL to a datawarehouse.
In case someone wonder, in this case, TIMESTAMP behave correctly and you can differentiate between the two similar dates by converting the TIMESTAMP to unix timestamp:
select TestFact.*, UNIX_TIMESTAMP(recordTimestamp) from TestFact;
id recordTimestamp UNIX_TIMESTAMP(recordTimestamp)
1 2012-11-04 01:00:10.0 1352005210
2 2012-11-04 01:00:10.0 1352008810
I was working on logging counts of visits of pages and displaying the counts in graph (using Flot jQuery plugin). I filled the table with test data and everything looked fine, but I noticed that at the end of the graph the points were one day off according to labels on x-axis. After examination I noticed that the view count for day 2015-10-25 was retrieved twice from the database and passed to Flot, so every day after this date was moved by one day to right.
After looking for a bug in my code for a while I realized that this date is when the DST takes place. Then I came to this SO page...
...but the suggested solutions was an overkill for what I needed or they had other disadvantages. I am not very worried about not being able to distinguish between ambiguous timestamps. I just need to count and display records per days.
First, I retrieve the date range:
SELECT
DATE(MIN(created_timestamp)) AS min_date,
DATE(MAX(created_timestamp)) AS max_date
FROM page_display_log
WHERE item_id = :item_id
Then, in a for loop, starting with min_date, ending with max_date, by step of one day (60*60*24), I'm retrieving the counts:
for( $day = $min_date_timestamp; $day <= $max_date_timestamp; $day += 60 * 60 * 24 ) {
$query = "
SELECT COUNT(*) AS count_per_day
FROM page_display_log
WHERE
item_id = :item_id AND
(
created_timestamp BETWEEN
'" . date( "Y-m-d 00:00:00", $day ) . "' AND
'" . date( "Y-m-d 23:59:59", $day ) . "'
)
";
//execute query and do stuff with the result
}
My final and quick solution to my problem was this:
$min_date_timestamp += 60 * 60 * 2; // To avoid DST problems
for( $day = $min_date_timestamp; $day <= $max_da.....
So I am not staring the loop in the beginning of the day, but two hours later. The day is still the same, and I am still retrieving correct counts, since I explicitly ask the database for records between 00:00:00 and 23:59:59 of the day, regardless of the actual time of the timestamp. And when the time jumps by one hour, I am still in the correct day.
Note: I know this is 5 year old thread, and I know this is not an answer to OPs question, but it might help people like me who encountered this page looking for solution to the problem I described.