PromQL
https://prometheus.io/docs/prometheus/latest/querying/basics/
Cheat sheet and Online
https://promlabs.com/promql-cheat-sheet/
https://demo.promlens.com/?q=rate(demo_api_request_duration_seconds_count%5B5m%5D)
Self playground
https://iximiuz.com/en/posts/prometheus-learning-promql/
https://github.com/iximiuz/prometheus-playground
tutorial
https://www.fosstechnix.com/prometheus-promql-tutorial-with-examples/