* InfluxDB: Send retention policy with InfluQL queries if it's been specified.
In InfluxDB v2, due to technical limitations of the InfluxDB v1
compatibility layer, retention policies in a query (e.g. "<retention
policy>.<measurement_name>") aren't honored and must be specified in the
URL query parameter `rp` to be applied. Grafana doesn't send this query
parameter which results in all queries resolving to the default
retention policy when querying InfluxDB v2 servers using InfluxQL.
This addresses the issue by sending the `rp` query parameter for queries
that have specified a retention policy in the `target` given to
`runExploreQuery`.
The outcomes are:
1. InfluxQL queries executed against InfluxDB v2 databases will have the
necessary retention policy information for queries like `SHOW FIELD
KEYS FROM measurement` to function correctly.
2. InfluxQL queries executed against InfluxDB v1 databases will be
unaffected, because this `rp` query parameter is unsupported there.
You can read more about the rentention policy mapping behavior of
InfluxDB v2 in our documentation:
- https://docs.influxdata.com/influxdb/v2.6/reference/api/influxdb-1x/dbrp/#when-querying-data
- https://docs.influxdata.com/influxdb/v2.6/reference/api/influxdb-1x/query/#query-a-non-default-retention-policy
* Use the ? operator
Co-authored-by: Ryan McKinley <ryantxu@gmail.com>
Co-authored-by: Ryan McKinley <ryantxu@gmail.com>
