Support timezone for a user-friendly way of setting the timezone offset

[jsternberg]

From a conversation in #2074.

We should support a more user-friendly way to set timezone offsets. In 0.13, you will be able to set an offset with an extra parameter in the GROUP BY time(...) section like this:

SELECT mean(value) FROM cpu WHERE time > now() - 7d GROUP BY time(1d, -5h)

It should also be possible to set this timezone offset through doing something like this:

SELECT mean(value) FROM cpu WHERE time > now() - 7d GROUP BY time(1d) TZ("America/New York")

This should automatically set the group by offset and could potentially be used for something else like handling daylight savings time switches.

[giko45]

note that using a offset and using TZ("America/New York") is (should) not be the same

the TZ implementation requires
1: times in the database are in UTC
2: before the grouping: convert all "time"-s in to the required TZ
3: do the grouping (since "time" now is a local time grouping will handle DST, and yes this will imply one day per year with 23 h and one day with 25h but thats OK ). Here the offset syntax will not be able to handle DST
4: last step i am not totally sure: *Should the result be converted back to UTC? * in case of continues queries: yes, you don't want to save local times in you DB. In case of client queries: probably yes too. only return UTC times to the client. this just might seem a bit strange since you will get daily aggregated values att an offset in UTC. However its the clients responsibility to present this correct.

[jufemaiz]

Further to this, please do not conflate offsets with timezones.

https://spin.atomicobject.com/2016/07/06/time-zones-offsets/

[sebito91]

This feature would actually be incredible, our support model is traditional follow-the-sun and it's difficult for some remote users to mentally adjust for timezones. Explicit settings would help tremendously.

[sebastianherp]

+1

Timezone support is a must have. The offset allows to handle that client side by changing the query depending on DST/TZ, but it really should be handled on the server to support queries that have an offset change in the middle of the selected time range.

[inselbuch]

has this been removed in 1.5?