The scope of ETL in data warehouse is very wide. Extracting data from data sources is called ETL, cleaning and analyzing the extracted data is called ETL, and loading the cleaned and analyzed results into other databases is also called ETL. There are many tools for ETL, so there are many technologies involved.

As for books, you can check the ETL toolbox of the data warehouse to understand what ETL does first. In terms of technology, it depends on what tools the company or project uses and what technology it learns. In addition, Baidu can search "big data field of lxw", which contains some articles about data warehouse and ETL.