Walkthrough has an example that may be inadvisable about sql-mysteries HOT 3 OPEN

for an exploratory introduction to SQL, I think it's ok to leave out schema structure details like reasoning about query performance

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Thanks for your interest in the project! That specific example is given in the context of learning about the existence of UPPER and LOWER functions, so it's hard to know how to teach those to people without running the theoretical risk you identify. Do you have a suggestion?

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Adding a comment about that pitfall after the query. Or have a specific optional section at the end of that tutorial about performance considerations, if you feel it is too early to talk about those when UPPER and LOWER are introduced.

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