I create in my personal MySQL DB on qnap NAS a date field with the format yyyy-mm-dd.
Sometimes I need to insert in this field date in the form 1880-00-00.
If I use a qnap phpAdmin app to connect to DB through browser I correctly see the value 1880-00-00.
But if I use a client like DBVisualizer, when I run the select on the db, in the data field I see 1879-11-30 rather than 1880-00-00.
How could I get the correct value I inserted in database?
1800-00-00 is not a valid date.
MySQL replaces it with a valid date value.
Here's an explanation of how this work behind the scenes:
1800-00-00 ==> 1799-11-30 -- substract 1 month and 1 day from valid 1800-01-01
1800-00-01 ==> 1799-12-01 -- substract 1 month from valid 1800-01-01
1800-01-00 ==> 1799-12-31 -- substract 1 day from valid 1800-01-01
1800-00-31 ==> 1799-12-31 -- substract 1 day from valid 1800-01-01
1800-01-01 ==> 1800-01-01 -- substract nothing, it's a valid date
If a date like 1800-00-00 is valid for you because you don't know month or a day when an event happened, you should consider changing your column type to varchar instead of date because in the future you are going to run into problems - especially when using ODBC. Those dates will be empty, as they are not known to that interface.
Of course, you have to be fully aware that you are giving up on building SQL queries that manipulate and calculate over date type (specific functions), but if your case is "more or less precise date" such queries wouldn't really give a stable result anyways.
Related
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.
I am using UNIX_TIMESTAMP(), but when I pass dates that are far in the future, it starts returning NULL at some point.
For example, the following SQL gives me a proper, non-null result: SELECT UNIX_TIMESTAMP(ADDDATE(NOW(), INTERVAL 18 YEAR)).
However, if I increase that value by one year, the returned value becomes NULL: SELECT UNIX_TIMESTAMP(ADDDATE(NOW(), INTERVAL 19 YEAR))
What is the problem here? Could it be an integer overflow? And how do I solve it?
I am using the following MariaDB version: Ver 15.1 Distrib 10.4.7-MariaDB, for Linux (x86_64) using readline 5.1
Unix time (signed 32-bit) ends on 03:14:07 Tuesday, 19 January 2038 UTC
Related: Year_2038_problem
UNIX_TIMESTAMP:
Timestamps in MariaDB have a maximum value of 2147483647, equivalent to 2038-01-19 05:14:07. This is due to the underlying 32-bit limitation. Using the function on a date beyond this will result in NULL being returned. Use DATETIME as a storage type if you require dates beyond this.
SELECT ADDDATE(NOW(), INTERVAL 19 YEAR) -- DATETIME
-- 2038-09-07 18:42:39
As stated in my above comment I couldn't make it work passed the 2038 Epochalipse date limit, not even converting the field to DATETIME. There are probably other considerations affecting this eventual solution.
The only workaround that I could find was to get the date out of the DB from PHP and use the strtotime() PHP function to get the UNIX TIMESTAMP from it.
SELECT DATE_FORMAT(CONVERT(thedatefield, DATETIME),"%Y-%m-%dT%TZ") AS thedatefield
As there exist different date formats (American, English, Latin, etc...) which are incompatible and a possible source of trouble, I am using two MySQL/ MariaDB functions to flatten the output to an ISO date (YYY-MM-DDThh:mm:ss). Once the output is uniform in any system you can pass the output to the strtotime() PHP function with the confidence that it will be correctly parsed to a UNIX TIMESTAMP.
CONVERT: casts the date to a datetime DB type.
DATE_FORMAT: converts the date to ISO format (YYY-MM-DDThh:mm:ss).
You can of course remove those functions and adapt the solution to the particularities of your system to reduce the processing load. This proposed solution will work with any system date style.
In case of just one register being returned by PHP (the simplest case) I set the first dimension of the returned 2D or table array to 0
date("U",strtotime($php_array[0][thedatefield]))
The PHP date() function by virtue of the "U" flag will convert the DB output to a UNIX TIMESTAMP without the 32 bit 2038 Epochalipse limitation.
I am trying to use a variable to increment a time variable used in a stored sql procedure.
I have tried
v_start1 = addtime(v_start1, v_inc);
where:
declare v_start1 Time;
declare v_inc time; or declare v_inc varchar(10);
select start1 from table into v_start1;
select inc from another_table into v_inc;
and it fails to increment v_start1
If I use v_start1 = addtime(v_start1, '00:15:00') it works but 00:15:00 is a fixed value that needs to be changed
How do I go about using a second variable to supply the value to increment v_strar1 by
How do I convert varchar to time; the value may be in the form +00:15 as a string
Are the values coming from "another_table" strings like "+00:15" or Time data type values? This may be a problem.
I would recommend that you avoid using strings and only deal with them as either time or datetime data types. If you have a string like "+15:00" it may mean 15 minutes but it looks to some people like 15 hrs. Maybe in your query the value in the table is a string and is not getting converted correctly. Get it into the table as a Time field and it should work.
As a side note I like to work with a full DATETIME data type rather than Time types like you are doing when I have the need to add/subtract. If you are really only interested in Time, then just use the current day-month-year with your incoming time.
I am not 100% sure for MySql, but for SqlServer and Oracle it is possible to run into the following scenario:
If v_start1 is 23:55:00 and you add 15 minutes it actually becomes 00:00:10 of the next day. If you add 1455 minutes you get the exact same time but 2 days later. So, just looking at Time can get you in trouble.
If you deal with a DATETIME type then you can always use DATE_ADD and add whatever seconds, minutes, etc. easily.
In MySQL, I am trying to get difference between two timestamp value and storing the result in time column. But sometimes the result comes in 'hhh:mm:ss' format. While trying to access that column in Java using Result.getTime(), it is throwing error saying 'Bad format for time in column x'.
To get better idea, store the result of following query in time column and try to access this value in Java.
SELECT SEC_TO_TIME(ABS(TIMESTAMPDIFF(SECOND,'2013-01-26 19:03:48','2013-02-15 06:59:36'))) as 'RESULT';
What should I do to get result even if it has 'hhh:mm:ss' format (without any error)?
Thanks in advance.
I assume you run query and result set contain the result
String hourMinSec=resultset.getString("RESULT");
String[]result=hourMinSec.split(":");
int hour=Integer.parseInt(result[0]);
int min=Integer.parseInt(result[1]);
int second=Integer.parseInt(result[2]);
Expressing difference between two dates as date is meaningless i think. Just to answer your question if you want to create time you can use following
Time time =new Time(hour, min, second);
But i feel its meaningless.
You can't express the difference between two dates as another date. For example if you will got 31 days difference you can't say if it is 1 month or 1 month and 1 day.
You should create your own object to storage this data.
The main problem is, that I have stored in database datetime , not the date (what I need). Ok never mind.
I have thousands of reports stored each day.
I need to LEFT by 10 my datetime_view (to cut the time) and everything's fine. Except this. I'm trying to figure out why do I have to put in the condition + one day from the future? Otherwise it won't search what I want.
SELECT
LEFT(datetime_view,10),
count(type)
FROM reports
WHERE
type IN (1,2,5)
AND
datetime_view>='2012-10-28'
AND
datetime_view<='2012-11-04'
group by LEFT(datetime_view,10);
You can see I must search from the future. Why??
It gives me an output from 28.10 to 3.11 ....
don't use string operations on date/time values. MySQL has a huge set of functions for date/time manipulation. Try
GROUP BY DATE(datetime_view)
instead, which will extract only the date portion of the datetime field. Your string operation is not y10k compliant. Using the date() function is.
As for your plus one day, consider how the comparisons are done: A plain date value, when used in date/time comparisons, has an implicit 00:00:00 time value attached to it, e.g. all dates have a time of "midnight".
i think it's better to use DATE(datetime_view) to cut the time instead of LEFT(datetime_view,10), also on the where condition:
DATE(datetime_view) <= '2012-11-03'