How to write custom queries using vertica-grafana plugin

Hi. If you supply some details on what you want or are trying to do I may be able to help answer the questions or submit requests for any that end up being limitations.
Some specific questions regarding the two questions:
time format - Grafana only recently added ability to control at a server level the format using the date_format section of the grafana.ini. It wasn't clear from your question if you are converting the time format in Vertica or elsewhere o please supply details.
group by - we do support using group by in the sql query , e.g.
select $__time(c1),c2,sum(c3) from testtime group by c1,c2;
but currently we do not support using the $_interval global variable to simulate group by using the interval pulldown menu.