Why does retention matter?
Retention shows how many users come back after their first visit. It’s the heartbeat of product growth - without returning users, there’s no compounding effect.
What usually goes wrong?
• Analysts mix new and returning users in the same metric
• Retention is counted without anchoring to cohorts
• Time frames aren’t aligned, so “day 7 retention” becomes meaningless
How do window functions help?
SQL lets you anchor users by their first activity date and then track if they return in following days or weeks. Window functions make it easy to:
• Define cohorts by first session date
• Compare activity across periods
• Ensure retention reflects true return behavior
What’s the practical move?
• Use MIN(event_date) to find first activity
• Calculate ratios of returning users per cohort
With this, retention becomes both accurate and actionable.
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