Build the safeguards
Eight explained steps, a source example and a checkpoint at each decision.
Read the tutorialPostgreSQL / Analytics / Data correctness
The dashboard looks right. The totals aren’t.
A query returns a neat table. Its revenue is inflated, its conversion rate counts events as people, and its reporting day misses an order. Find the definition behind each number.
The idea in plain language
A correct report begins with a precise definition of one row, one eligible person and one reporting period. SQL can execute perfectly while answering the wrong business question.
Actual PostgreSQL runs through the open-source PGlite runtime in a fresh in-memory worker. Four invented orders explain correctness. Their query plans do not establish warehouse cost, index benefits or production performance.
Your independent testing environment
Make the failure visible.
Start with duplicate revenue. Compare 42000 cents with 30000 cents and locate the repeated order. Then test experiment cohorts and the 25-hour New York reporting day.
Order 1 has two lines; revenue belongs to the order, not each joined line.
Ready. Choose an example and run both implementations.
Explain the result
Revenue is 42000 cents with the multiplying join and 30000 at order grain. The local-day example returns 26000 cents; the UTC-day query returns 24000. The safeguarded cohort has one A user and two B users.
Open the exact source behind this edition. The viewer checks each file against its SHA-256 manifest and explains the decision it implements.
Choose your next step
Compare the alternatives
Understand where each pattern helps and which tradeoffs remain.
Compare approachesRun and extend it locally
Download the independent environment, run the native checks and try a specific extension.
Open the how-to guideBefore you try it
Do I need to know how to code?
Start with Run and read the comparison. The tutorial introduces the code after you have seen the behavior. The how-to guide separates a no-install route from the native developer exercise.
What happens to the experiment when I reset?
Reset discards this lab’s temporary state and cancels or terminates its pending work. These examples use invented records. No account, production data or cloud deployment is needed.
What does the browser experiment establish?
Actual PostgreSQL runs through the open-source PGlite runtime in a fresh in-memory worker. Four invented orders explain correctness. Their query plans do not establish warehouse cost, index benefits or production performance.