I am always amazed by the expert mode of the SQLite CLI.

You type .expert
Then you paste your SQL query.
And #sqlite tells you which indexes you should create to speed up your query.

No AI, no complex program to install. No expensive database architect to pay for. It's just clever programming.

To my knowledge this is the only database in the world to have this feature.

https://sqlite.org/cli.html#index_recommendations_sqlite_expert_
https://sqlite.org/src/dir?ci=trunk&name=ext/expert