I've been using relational databases for web apps for my entire career and probably would have made this same mistake if using PlanetScale for the first time.
The author had two misunderstandings:
1) An index isn't created automatically
2) You get billed for the number of rows scanned, not the number of rows returned
Even if I noticed #1, I probably wouldn't have guessed at #2 for the same reason as the author.
The author had two misunderstandings:
1) An index isn't created automatically
2) You get billed for the number of rows scanned, not the number of rows returned
Even if I noticed #1, I probably wouldn't have guessed at #2 for the same reason as the author.