Document INTO keyword

[jackzampolin]

Originally: https://github.com/influxdb/influxdb.com/issues/520

Starting from version 0.9.5 INTO keyword can be used outside of continuous queries: influxdata/influxdb#4409.

But it's still unclear how to use this feature.

I was able to make two-step filtering with queries like these:

SELECT last(size) INTO temp FROM vm GROUP BY hostname
SELECT sum(last) FROM temp
But here are two questions:

1. how to join them into a single query? Semicolon does not work by some reason.
2. I'm using temp, but what does this syntax mean? It is some kind of a local variable? Is it performant and safe to use on a large number of queries in Grafana?

Thanks.