DateTime Data Types

bks

Hi,

What is the practical use of DateTime data type?

kriki

If you need to keep track of both the date and time of something, this can be useful. An example is a NAS that is logging its actions when they took place. In stead of using 2 fields, you can use only 1.

bks

Hey Kriki...

Thanks for the reply.

Please make me understand the concept of UTC and Daylight saving time with reference to DateTime data type.

kriki

UTC (=Universal Coordinated Time = GMT = Greenwhich Mean Time = Zulu Time [check http://www.timeanddate.com/worldclock/ can be useful).
All datetime are converted to this time.
It is useful in case people from allover the world are working on the same DB and have different timezones (or daylight saving time).
If at this very moment I write a CURRENTDATETIME to the DB, I will see 05/02/2008 14:01. If someone in the UK does it 1 minute after me, he will see 05/02/2008 13:02. And if someone in New York does it 2 minutes after me, he will see 05/02/2008 08:03.
If I want to order them in order of entry, New York would come first, then UK, then me (in case of normal date-time fields).
With Datetime-fields, this will not be the case:
I will see 14:01 for me, 14:02 for UK and 14.03 for New York.
If someone from the UK checks at the same moment, he will see 13:01 for me, 13:02 for UK and 13:03 for New York.
If someone from New York checks at the same moment, he will see 8:01 for me, 8:02 for UK and 8:03 for New York.

And the records will be in the correct order (the order of entry ; and NOT the LOCAL date and time).

I hope this is clear now.

BTW : also the datetimes of the posts on Mibuso are saved as UTC and in your settings, you put in which timezone you want to see them.

jreynolds

You should pay particular attention to the help topic on the DateTime data type with respect to how it is stored as UTC and the particular issues associated with time zones and daylight saving time. This makes it great for logging when an activity occurred (e.g. change log). However, you need to be very careful how you use it in other contexts. For example, if you were to use it to schedule an event for 8:00 AM next Monday and it so happened that the daylight saving change happened on the intervening Sunday then the event would actually happen at 7:00 or 9:00 (depending on the direction of the change).

andy76

Hello everybody,

In Job Scheduler of NAV 5.0 I could set some server for different customers to execute some report and codeunit different and it runs right.

The problem that I found in these days is that having changed the hour from
2:00 a.m. to 3:00 a.m in the night between 29 and 30 March all my scheduled
activities have been delayed of an hour.
Now I resetted them (in job queue entry card) and restarted the application
server and it seems to go at the right time but the problem can happen again
every 5-6 months when the time is changed.
Is it possible to solve this problem? How?

Thank you very much

kriki

The only way to solve it is NOT to use a datetime field (and neither a time-field on SQL because date,datetime,time are converted to datetime on SQL. And datetime depends on the timezone and also winter/summertime. If you don't want to be influence by it, you need to use another datatype like integer.