SQL
Index selectivity
How do lessons work?
- Lessons are small steps: short explanations, questions and coding tasks.
- Answer and press Check (Enter); steps you miss come back at the end.
- In coding tasks, type in the editor and the preview or console updates instantly.
- Stuck? Press Hint (H); Lesson notes show the whole lesson as a readable page.
- Spot a mistake? Report an issue sends us the step details.
query.sql
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Expected output
Something wrong here?
The lesson and step are added automatically.