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InfluxDB
Power Real-Time Data Analytics at Scale. Get real-time insights from all types of time series data with InfluxDB. Ingest, query, and analyze billions of data points in real-time with unbounded cardinality.
Specifically for ABAP, there is just one free SAP course for beginners. It is a decent course but it does not really teach classic ABAP that you're probably encountering if you're working with an on-premise system. For classic ABAP, to be honest, there is no better source than my own book. :) It was written for complete beginners, explains very basic IF... THEN... stuff. I've heard from many functional consultants who used it to learn ABAP and so far no unhappy customers. The book is also recommended by ABAP Starter.
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