Grafana has almost no query language of its own - it supplies values such as
__from __to and $__timeFilter but the underlying capabilities of the queries
you can run are entirely determined by the back-end data store (in your case,
This is because Grafana creates queries, but it then runs those queries on the
data store, so you can only do what the data store language supports.
The MySQL query you point to uses the date() function in MySQL to identify one
day as distinct from the next, and I do not believe this function exists in
Influx’ query language.
If you can use Influx2 you might find that FluxQL supports what you want to do,
but I’m not familiar with that so I cannot say for certain - hopefully someone
else here with experience of FluxQL can step in and confirm.