Add support for `get` / `show` timezone

[avantgardnerio]

Is your feature request related to a problem or challenge? Please describe what you are trying to do.

Presently, show timezone does not work:

DataFusion CLI v11.0.0
❯ show time zone;
NotImplemented(“SHOW time.zone not implemented. Supported syntax: SHOW <TABLES>“)

Describe the solution you'd like

Instead, I would like:

show timezone;

To always return 'utc'.

set timezone 'utc';

Should succeed.

set timezone 'UTC+08`;

should return an error.

and

set timezone 'US/Mountain`;

should return the same error.

This should:

1. make the work @waitingkuo is doing easier by ignoring non-UTC zones for now
2. Stay technically compatible with ANSI SQL & postgres (as long as postgres is set to UTC)
3. allow the option to implement timezones at a future date.

PS:

Do the same for select current_setting('TIMEZONE')

Describe alternatives you've considered

• Having to violate ANSI SQL
• Having to tackle timezones while implementing timestamp without timezone

[avantgardnerio]

@andygrove @waitingkuo @alamb @tustvold

[alamb]

For what it is worth, here is what postgres does (mostly what @avantgardnerio has proposed). Note there is an = in SET TIMEONE='';

psql (14.4)
Type "help" for help.

alamb=# show timezone
alamb-# ;
     TimeZone     
------------------
 America/New_York
(1 row)

alamb=# set timezone='UTC+08';
SET
alamb=# show timezone;
 TimeZone 
----------
 UTC+08
(1 row)

alamb=# set timezone='US/Mountain';
SET
alamb=# show timezone;
  TimeZone   
-------------
 US/Mountain
(1 row)

[alamb]

(the proposal in this ticket sounds good to me)

[avantgardnerio]

Nice work @waitingkuo , thank you!!