Compute signup rate and retention from raw logs

Scenario

You are analyzing an A/B test for a marketing campaign offering a free 1-month trial.

You are given raw “upstream” tables that resemble production event logs rather than pre-aggregated metrics.

Assume UTC timestamps and that each user has at most one assignment.

Tables (upstream)

experiment_assignment

• user_id (STRING, PK)
• experiment_id (STRING)
• variant (STRING; 'control' or 'treatment')
• assigned_at (TIMESTAMP)

offer_exposure_events

• user_id (STRING)
• exposed_at (TIMESTAMP)
• campaign_id (STRING)

subscription_events

• user_id (STRING)
• event_time (TIMESTAMP)
• event_type (STRING; one of 'trial_start', 'paid_start', 'cancel')

app_sessions

• user_id (STRING)
• session_start (TIMESTAMP)

Metric definitions

1. Signup rate (trial start within 7 days)

• Denominator: users assigned to the experiment.
• Numerator: users with a trial_start event where event_time is in [assigned_at, assigned_at + 7 days).

1. D30 activity retention Among users who started a trial within 7 days, the user is retained if they have ≥ 1 app session with session_start in [assigned_at + 30 days, assigned_at + 37 days).

Task

Write SQL to output one row per variant with:

• variant
• assigned_users
• signup_users_7d
• signup_rate_7d
• retained_users_d30
• retention_rate_d30

Also briefly describe what an “upstream” dataset/logging pipeline must contain to compute these metrics reliably (e.g., assignment logs, exposure logs, subscription lifecycle events, identity consistency).