[rodrigoi]

Problem

#61796 introduced metric-event breakdown attribution for funnel metrics. Mean metrics still attribute the breakdown from the exposure event, with the same null-bucket and consistency problems.

Changes

This PR migrates mean metrics to MetricBreakdownInjector, still behind the experiment-metric-event-breakdowns flag.

Mean support in the injector

Mean metrics have no attribution modes, so the breakdown is always first touch: argMin over the metric event timestamp per user. The conversion window is already enforced by the entity_metrics join, so no extra condition is needed. The injector's constructor now accepts all metric types; the funnel-only _attribution_step asserts it only runs for funnels.

Session-property metrics

Session-property means have an extra metric_events_by_session layer whose metric_events CTE joins exposures and can't see raw event properties. The breakdown is read and deduped per session in the by-session layer (via any()), then carried up with first_event_timestamp so attribution uses the session's first event time.

Winsorization

Winsorized means carry the breakdown through the percentiles and winsorized_entity_metrics CTEs, preserving per-breakdown-group thresholds. Top-N ranking is always computed from entity_metrics since winsorization doesn't change the set of (entity, variant, breakdown) tuples; _inject_final_breakdown_columns learned a final_cte_name so the outer SELECT reads from the right CTE.

Wiring

Mean joins the migrated set in the runner. Both injectors expose inject_mean_breakdown_columns, so the mean builder calls whichever it was given without type checks.

• products/experiments/backend/hogql_queries/metric_breakdown_injector.py
• products/experiments/backend/hogql_queries/experiment_query_runner.py
• products/experiments/backend/hogql_queries/experiment_mean_query_builder.py

Tests

test_metric_breakdown.py starts the flag-on runner suite (funnel and mean paths, including session properties and winsorization); injector unit tests cover the new AST shapes. The flag-off suite in test_breakdown.py stays as the old-path regression guard.

• products/experiments/backend/hogql_queries/test/experiment_query_runner/test_metric_breakdown.py
• products/experiments/backend/hogql_queries/test/experiment_query_runner/test_breakdown.py
• products/experiments/backend/hogql_queries/test/test_metric_breakdown_injector.py

How did you test this code?

pnpm turbo run backend:test --filter=@posthog/products-experiments

👉 Stay up-to-date with PostHog coding conventions for a smoother review.

Automatic notifications

• Publish to changelog?
• Alert Sales and Marketing teams?

Docs update

🤖 Agent context

Autonomy: Human-driven (agent-assisted)

Model: Opus 4.7 (implementation), Fable 5 (restack and PR description)
Manually refactored: yes

Skills used:

• /writing-plans (superpowers)
• /writing-tests (local)
• /writing-pull-requests (local)

Relevant decisions:

• Mean attribution is fixed first touch from the metric event, with no user-facing modes; funnels are the only type where an attribution choice is meaningful.
• Winsorization thresholds are computed per breakdown group (unchanged from the old injector), and top-N ranking deliberately reads pre-winsorization entity_metrics.
• Session-property breakdowns are deduped with any() per session, mirroring how session_value is computed.

[rodrigoi]

Warning

This pull request is not mergeable via GitHub because a downstack PR is open. Once all requirements are satisfied, merge this PR as a stack on Graphite.
Learn more

• feat(experiments): add ratio metrics to the metric breakdown injector #62293
• feat(experiments): add retention metrics to the metric breakdown injector #62292
• feat(experiments): add metric breakdown injector for mean metrics #62291 👈 (View in Graphite)
• feat(experiments): add metric breakdown injector for funnels #61796
• feat(experiments): add breakdown attribution to the metric row group #61788
• master

This stack of pull requests is managed by Graphite. Learn more about stacking.

[greptile-apps]

Comments Outside Diff (1)

1. products/experiments/backend/hogql_queries/metric_breakdown_injector.py, line 1-13 (link)

   The module docstring still says "Scope: funnel metrics only" but mean metrics were just migrated here, and MetricType already includes ExperimentRatioMetric and ExperimentRetentionMetric in the union for future migrations. The scope line and first-paragraph framing no longer reflect the file's actual responsibility.

   Prompt To Fix With AI

   This is a comment left during a code review.
   Path: products/experiments/backend/hogql_queries/metric_breakdown_injector.py
   Line: 1-13
   
   Comment:
   The module docstring still says "Scope: funnel metrics only" but mean metrics were just migrated here, and `MetricType` already includes `ExperimentRatioMetric` and `ExperimentRetentionMetric` in the union for future migrations. The scope line and first-paragraph framing no longer reflect the file's actual responsibility.
   
   How can I resolve this? If you propose a fix, please make it concise.

   Note: If this suggestion doesn't match your team's coding style, reply to this and let me know. I'll remember it for next time!

Prompt To Fix All With AI

Fix the following 1 code review issue. Work through them one at a time, proposing concise fixes.

---

### Issue 1 of 1
products/experiments/backend/hogql_queries/metric_breakdown_injector.py:1-13
The module docstring still says "Scope: funnel metrics only" but mean metrics were just migrated here, and `MetricType` already includes `ExperimentRatioMetric` and `ExperimentRetentionMetric` in the union for future migrations. The scope line and first-paragraph framing no longer reflect the file's actual responsibility.

_{Reviews (1): Last reviewed commit: "feat(experiments): add metric breakdown ..." | Re-trigger Greptile}

[trunk-io]

   

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[andehen]

Findings from a review of the full stack (#61788, #61796, #62291, #62292, #62293), placed on the PR where each belongs. Prefixes: should-fix, suggestion, nit.

[scheduled-actions-posthog]

This PR hasn't seen activity in a week! Should it be merged, closed, or further worked on? If you want to keep it open, please remove the stale label – otherwise this will be closed in another week. If you want to permanently keep it open, use the waiting label.

[scheduled-actions-posthog]

This PR hasn't seen activity in a week! Should it be merged, closed, or further worked on? If you want to keep it open, please remove the stale label – otherwise this will be closed in another week. If you want to permanently keep it open, use the waiting label.

[scheduled-actions-posthog]

This PR hasn't seen activity in a week! Should it be merged, closed, or further worked on? If you want to keep it open, please remove the stale label – otherwise this will be closed in another week. If you want to permanently keep it open, use the waiting label.