Found 2 comments on HN
boshomi · 2019-02-15 · Original thread
@MarkusWindand: Thank you for the Websites [1],[2],[3] and the book »SQL Performance Explained«[4].

[1] https://modern-sql.com/

[2] https://use-the-index-luke.com/

[3] https://db-engines.com/

[4] https://www.amazon.de/SQL-Performance-Explained-Everything-p...

adamnemecek · 2017-01-19 · Original thread
If this tickles you fancy, you should check out this site http://use-the-index-luke.com or a book by the same author https://www.amazon.com/Performance-Explained-Everything-Deve...

He goes into great detail to explain how exactly SQL indices work and how to leverage this to write queries.

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