ETL: ETL (extract, transform, and load) is a process that involves extracting data from an external source, altering it to meet operational requirements (often utilizing staging tables), and then putting it into the ultimate target database or data warehouse. As long as your data warehouse landscape includes a variety of databases, this strategy is appropriate. Because you must transmit data from one location to another in this case, it is a valid option to do the transformation job in a separate specialized engine.
ELT: ELT (Extract, Load, Transform) is a procedure in which data is extracted, then loaded into a database staging table and transformed. Then it’s loaded into the target database or data warehouse, depending on where it’s stored in the database.