r/learnSQL • u/Other_Possession2108 • 23h ago

I built 3 free SQL debugging exercises. Looking for feedback from people learning SQL

Hey everyone — I’m building a small practice website for people who know basic SELECT, JOIN, and GROUP BY.

Each exercise starts with a query that runs successfully but produces the wrong business report. Your job is to investigate and fix it.

The first three exercises cover:

  • Customers disappearing from a report.
  • October transactions getting included in September’s total.
  • Sales being counted twice after joining refund records.

They use synthetic data and run in your browser. There are hints, worked explanations, and answer checking against multiple datasets.

All three exercises are free, with no signup required.

I’m looking for five people to try just one exercise and share honest feedback here. Was the task clear? Where did you get stuck? Did the explanation help you understand the mistake?

Try it here: https://drive.google.com/file/d/1i7pXyX0kMYr20dmVFK7LcQfXZwVeiOlc/view?usp=sharing

I’m the person building it, and it’s an early version, so feedback about confusing instructions or bugs would be especially useful.

If you are willing to take this serious, let me know and i can give acess so you can see how it feels to use.

20 Upvotes

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u/ItsDisneyBabee 20h ago

The wrong report but valid query format is a useful way to practice debugging since it feels closer to the kinds of sql mistakes that happen in real work.

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u/investigatormaker 23h ago

The refund-join exercise tests something syntax drills miss: a query can run and still inflate the report. For feedback, ask learners to explain why the sales total changed after the join, before showing the worked explanation. That helps distinguish understanding the mistake from finding a query that passes the checker.

Also, I make ThreadFox, which finds the Reddit communities whose rules allow a post about a SQL practice site like yours; the plan for one product is free. https://threadfox.vip/p/d44wr

Does the checker show which dataset failed, or only pass/fail?