Run broken down analyses in one SQL query like others

[Twixes]

Changes

Currently our ClickHouse analyses require an additional SQL query when using breakdown – for obtaining values to break down by. This impact speed and therefore user experience, because an additional query round trip before the proper query takes time. We can do away with this using common table expressions though – this way the same breakdown values query is ran before the proper analysis one all in the same query string.

Checklist

• All querysets/queries filter by Organization, by Team, and by User
• Django backend tests

[neilkakkar]

Heads up: I'd like this to go in after #5043 which introduces some tests for breakdown keys having different types (possible with JsonExtractRaw), just to ensure things keep working with this change :)

[macobo]

Fly-by comment

This impact speed and therefore user experience, because an additional query round trip before the proper query takes time.

Note that this is not always true. More roundtrips can often end up faster if you can optimize the amount of data being sent back or how the query executes as a result. E.g. if you're fetching a collection of size N and collection of size M separately it can be much better than trying to fetch N x M.

A good example of this is how our sessions query works - fetching relevant users -> sessions is much faster than trying to do an inline join in practice because we can set limits on what data to look at and when to stop iteration early.

In practice UX has been affected by queries taking 5 seconds + - one vs two sync_execute matters very little here. It's worth being principled and measuring the effect.

All of that said I haven't dug into the diff - it sounds like it might be a valid optimization. I'd just be wary of generalizing like above. :)

[Twixes]

No no @macobo, this is literally the same performance wise as with roundtrip, only the roundtrip is eliminated with a CTE. No joins, it's just basically saving the values to break down by as a variable inside ClickHouse before the final query.

[Twixes]

Opening a new PR as I'm more confident about doing this on top of master than about reconciling these pretty big merge conflicts.