Support inline stats about elasticsearch HOT 3 OPEN

Pinging @elastic/es-analytical-engine (Team:Analytics)

from elasticsearch.

We're planning to implement this by splitting the query into two commands internally, then running them in a row. So, this:

FROM foo
| INLINESTATS MIN(b) BY a
| WHERE b == MIN(b)

becomes these two:

FROM foo
| STATS MIN(b) BY a

----and----
FROM foo
| LOOKUP _inlinestatsresults_ ON a
| WHERE b == MIN(b)

That LOOKUP command is being implemented here: #107987. It's my first step to getting this in.

from elasticsearch.

The main limitation of this approach is that the results of the first STATS result has to be small enough you can push it across the wire. That's going to be true in plenty of cases, but at some point we'll need to deal with results that don't fit. Those cases are harder and probably all want some ability to spill to disk.

from elasticsearch.