Grafana has global built-in variables that can be used in expressions in the query editor.
### Time range variables
Grafana has two built in time range variables in `$__from` and `$__to`. They are currently always interpolated
as epoch milliseconds.
### The $__interval Variable
This $__interval variable is similar to the `auto` interval variable that is described above. It can be used as a parameter to group by time (for InfluxDB, MySQL, Postgres, MSSQL), Date histogram interval (for Elasticsearch) or as a *summarize* function parameter (for Graphite).