I have a condition qa.actual_date >= today - 1 in a informix query.
Does it fetch the records exactly from the past 24 hours?
Eg:
Curent date and time is 13 Jun 2019 12:45 PM
does qa.actual_date >= today - 1 will fetch the records from 12 Jun 2019 12:45 PM or 12 Jun 2019 12:00 AM
Under Informix, a DATE value refers to a day, and has no explicit time component. Given a current date of 2019-06-13 and assuming the type of qa.actual_date is DATE (and not a DATETIME type), the condition:
qa.actual_date >= TODAY - 1
selects all records where the qa.actual_date value is (any time on) 2019-06-12 or later.
If qa.actual_date is of type DATETIME YEAR TO SECOND or any other type that has an hour, minute, or second component (as well as day, month, year components), then the value of TODAY - 1 will be converted (extended) to that type, and the missing time components will be treated as zeroes.
SELECT EXTEND(TODAY - 1, YEAR TO SECOND) FROM sysmaster:sysdual;
That will return 2019-06-12 00:00:00.
Related
I'm a bit confused about this outcome, taking today's date minus 2 months, and then taking that date again and adding two months, does not give me today's date when assign the dates to a variable.
Time.zone
"Eastern Time (US & Canada)"
> today = Date.today.in_time_zone
=> Thu, 31 Aug 2017 00:00:00 EDT -04:00
> a = today - 2.months # This is persisted to the db
=> Fri, 30 Jun 2017 00:00:00 EDT -04:00
> b = a + 2.months
=> Wed, 30 Aug 2017 00:00:00 EDT -04:00
If I however, just use the same object, it moves back and forth properly:
> today = Date.today.in_time_zone
=> Thu, 31 Aug 2017 00:00:00 EDT -04:00
> today - 2.months
=> Fri, 30 Jun 2017 00:00:00 EDT -04:00
> today + 2.months
=> Tue, 31 Oct 2017 00:00:00 EDT -04:00
The problem is obviously when "a" gets saved to a database, and then retrieved later on, and calculated plus 2 months..., it should match today's date.
TL;DR
A month is not a fixed duration. Adding or taking a month does not give the same "time shift" depending on which day you are.
The usual algorithm
to add or take months is the following :
try to land on the same day number (4th, 30th, 31st) as you started, just by changing the month
if you would land on an impossible date (like 31th September, 30th February, 29th February for some years) then just go the maximum allowed day number of this month
This implies that adding some months then taking out the same number of months will not necessarily give you back the same date.
Examples :
31st of some month + 1 month --> One would want to get to the 31th of next month
But if there is no 31st of next month (like for 31th of August, no 31st of September), then what to do ?
Usual interpretation would say that you want to go to the end of the month, this is 30th September (for rent or other monthly subscription, for instance)
But usually, 30th of some month - 1 month --> One would want to get to the 30th of the previous month.
That would lead to .... 30th of August. Not 31th of August.
Hence: some date + 1 month - 1 month does not necessarily give the original date !
Another example :
Start at the 30th of August.
Take a month -> 30th of July
Add a month -> You want to get to 30th of August (same number, next month) or to the end of August ?
The default algorithm will try to give the same day number -> 30th of August (which is more logical now)
Also with days...
Note that the same problem happens with days,but much less often ! When some days don't have the same number of hours, for daylight saving days, when adding and taking same number of days you might not get back to the original date and time as you started from.
Informix is not my normal environment and the way it handles datetime values is throwing me for a loop. I can't imagine this is difficult, but for the life of me I'm not yet able to figure it out.
This is the SQL:
SELECT agentid,
extension As Ext,
resourcefirstname As FirstNm,
resourcelastname As LastNm,
Min(eventdatetime) As FirstIn
FROM agentstatedetail AS asdr Join
resource As r On asdr.agentid = r.resourceid
WHERE asdr.eventdatetime BETWEEN '2016-10-20 04:00:00' AND '2016-10-21 03:59:59'
AND eventtype = 3
AND assignedteamid = 14
Group By agentid, extension, resourcefirstname, resourcelastname
Order By Min(eventdatetime)
Everything works as is, but the dates in the Between clause are currently entered manually- not optimal. I just need some way to describe "yesterday at 4:00 AM" and "Today at 4:00 AM" Will somebody please clue me in?
Using Informix version 12.10.FC6DE, I can do this:
SELECT
TODAY::DATETIME YEAR TO SECOND AS today_zerohour
, TODAY::DATETIME YEAR TO SECOND - '20:00:00'::INTERVAL HOUR TO SECOND AS yesterday_dawn
, TODAY::DATETIME YEAR TO SECOND + '04:00:00'::INTERVAL HOUR TO SECOND AS today_dawn
FROM
systables
WHERE
tabid = 1;
And it returns:
today_zerohour yesterday_dawn today_dawn
2016-10-21 00:00:00 2016-10-20 04:00:00 2016-10-21 04:00:00
So, what is happening here:
The operator TODAY returns the system date as a DATE type. The DATE type does not have the precision I want (it only has year, month and day), so I cast the value (cast operator is ::) to a DATETIME with precision from year to second (the hour, minutes and seconds are set to zero):
TODAY::DATETIME YEAR TO SECOND
In Informix, for an addition or subtraction with a DATETIME value to return another DATETIME value, I need to add or subtract an INTERVAL value. So I created 2 INTERVAL values.
One INTERVAL of 20 hours to subtract from the today value (again the cast operator :: is used, this time to cast from a string to an INTERVAL):
'20:00:00'::INTERVAL HOUR TO SECOND
One INTERVAL of 4 hours to add to the today value:
'04:00:00'::INTERVAL HOUR TO SECOND
I want to know How do I find the date offset from beginning of year in iOS. I want a function which will take the date as an input and tell me the number of days passed.
For ex Jan 2 = 2nd Day of year and Feb 14 = 45th Day of Year
Delphi Xe, Win 7, System TimeZone UTC+4:0, The first day of week in system - Monday, Time is synchronised with time.windows.com
In a palette of standard components Delphi Win32 there is component MonthCalendar, at it property WeekNubers=true (display of numbers of weeks), date=now, the first day - Monday.
Shows on 19 number (today) - number of week 43.
I request number through dateutils.WeekOfTheYear(now) = returns 42.
Source (0.5 Mb) http://www.sendspace.com/file/yuz6ko
Judging by an initial code of component MonthCalendar - there like all it is true (even if not to expose the first day of week, it takes value from system parametres).
And in inquiry WeekOfTheYear it is told, that all is considered also standard ISO applied, but numbers do not coincide :(
In any way I will not understand, where one week disappears - if to look on a calendar, should be 43 and if to consider, that weeks 53 and the first concerns last year...
By the way WeekOfTheYear on 01.01.2011 too returns 52 though like should return 1...
Why distinctions and where it is correct?
Both results are correct, the difference is because the DateUtils.WeekOfTheYear function uses the ISO 8601 standard definition of a week. That is, a week is considered to start on a Monday and end on a Sunday.
Check this explanation about the Weeks Numbers in the ISO 8601 format.
If 1 January is on a Monday, Tuesday, Wednesday or Thursday, it is in
week 01. If 1 January is on a Friday, Saturday or Sunday, it is in
week 52 or 53 of the previous year (there is no week 00). 28 December
is always in the last week of its year.
Also the Embarcadero online help for the DateUtils.WeekOfTheYear function says
....if the first calendar day of the year is a Friday, Saturday, or
Sunday, then for the first three, two, or one days of the calendar
year, WeekOfTheYear returns the last week of the previous year.
Similarly, if the last calendar day of the year is a Monday, Tuesday,
or Wednesday, then for the last one, two, or three days of the
calendar year, WeekOfTheYear returns 1 (the first week of the next
calendar year).
So due which the 01-01-2011 was Saturday this week is considered the week number 52 of the previous year.
And that also explains why the week number returned for today (19-10-2011) is 42 instead of 43.
First of all, I could see no difference between the week numbers in the TMonthCalendar component and those returned by DateUtils.WeekOfTheYear(). (Monday is the first day of week on my system.) Both show 42 for the current week and 52 (not 53) for the week of 2011-01-01. (It's 53 for 2010-01-01, so maybe you just mixed that up.)
Now, as to why it's 52 or 53, but not 1, well, it's according to the definition of the first week by ISO:
First week is the week with the year's first Thursday in it.
So week number 1 in 2011 starts on 2011-01-03, and the previous one belongs to the previous ISO year.
The TMonthCalendar can treat the last week of the year as the first week of the next year, WeekOfTheYear function does not do it, hence the difference.
For example according to TMonthCalendar, 1 Jan 2012 belongs to both last week of 2011 and first week of 2012; 2 Jan 2012 is the first day of the second week of 2012.
According WeekOfTheYear function, 1 Jan 2012 belongs to the last week of 2011 only; 2 Jan 2012 is the first day of the first week of 2012.
Monday is the first day of the week for me.
How do I return information in rank of closeness to the current date irrelevant of the year. If Current date is May 26 2011, the date closeness to May 26 is returned first. My problem was this confusion: I have two dates: Date 1: May 24th 2011 and Date 2: June 1st 2010, ensuring that Date 2 is returned before Date 1. Both because May 24 has passed and also the year factor.
Table:
Name Created_at
Bob 2010-06-01 (YYYY-MM-DD)
Mike 2010-05-07
Fife 2011-05-09
So it would return if current date is May 26 2011:
Bob 2010-06-01 (YYYY-MM-DD)
Mike 2010-05-07
Fife 2011-05-09
What I have so far:
#awesomeDate = Names.order("name").having("date > ?", Date.today)