Expression aggregations

[salsakran]

We should allow the equivalent of druid post aggregations to do things like divide a result by a constant or once #3364 is in place calculate things like averages.

[underyx]

This would make it possible to take a table like

source	visits	conversions
search	100	20
referral	200	10
direct	300	0

and query for sum(sales) / sum(users), to get the total conversion rate of 5%, right? Cause if so, I won't create a duplicate feature request for that 👯‍♂️

[jbelke]

v0.27.2 Built on 2017-12-12
Post Aggregates Failing.

custom expression
=Sum(¨Transaction Revenue¨) / Sum(Transactions)

If grouped by Timestamp, daily raw works.

Native Query:
{ "intervals":[ "1900-01-01/2100-01-01" ], "granularity":"all", "context":{ "timeout":60000 }, "queryType":"select", "pagingSpec":{ "threshold":1048576 }, "dataSource":"ChannelGrouping", "postAggregations":[ { "type":"arithmetic", "name":"AoV Test - ", "fn":"/", "fields":[ { "type":"fieldAccess", "fieldName":"___sum_549" }, { "type":"fieldAccess", "fieldName":"___sum_550" } ] } ], "descending":false }

[Octivian]

@jbelke v0.28.1 same issue