[yunqa.de] Re: Question about UTC and local time
- From: "Jerry Hayes" <jhayes@xxxxxxxxxxxxxxxxx>
- To: <yunqa@xxxxxxxxxxxxx>
- Date: Sat, 5 Jul 2008 08:11:49 -0400
If I have a value in Delphi which is of type TDateTime and equals to Delphi
function Now(). How to store this value to the DB correcty?
Edwin, (not Ralf here, but I’ll try to help ;)
I think you have 2 real options, since as it’s been stated, there’s no
native date type.
1. Store everything as a float, with the dates calculated to UTC before
storage. Since you’re at +8, all the stored values would be 8 hours off for
your time zone, you’d just have to have the local application realize that
they were. What you lose here is what the original time zone was, (unless
you store it in an additional field and have all your dates as two fields).
2. Store everything as text, with dates calculated to UTC before storage and
then add the time zone as text. YYYY-MM-DD HH:NN:SS.SSS *always* as UTC and
then add your zone information at the end +08, etc. So you get YYYY-MM-DD
HH:NN:SS.SSS ZZZ (where ‘Z’ is the time zone). One field, just more storage
bytes.
Either of these two give you a fixed point in time that can be accurately
indexed and compared – the first since it’s numeric, the second because the
date format is formatted so it can be compared. The key point in both
options is that you’re converting to UTC *before* storage.
HTH,
Jerry
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