Preserve denominator rows when calculating rates.
Live query triage Ben reports activation at 71 percent. Product asks why the denominator excludes users who never opened the app. The answer is an INNER JOIN buried three lines up. Each branch shows a consequence tied to SQL semantics. Symptom to semantics Rate queries are denominator queries first. If the base population disappears in FROM or WHERE, the final percentage can look precise and still answer the wrong question. LEFT JOIN, conditional aggregation, and explicit cohort CTEs make the denominator visible. Patch the syntax Fast but often wrong A query whose result matches the business claim. Fix the meaning…
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