The Not-So-Dark Art of Designing Database Indexes: Reflections from an Engineer

This is very good article detailing almost everything which almost every "not a dba, but still had to write queries" kind of backend developer has to do sooner or later.

Also, more index !== more performance. I think he explains it best : " If you need to access data quickly, you index it. If the performance of data (which almost always results in bloat) access isn't a concern, you don't index it"

This is an important topic that I believe is well explained here. Thanks !