ETL testing is one of the much in demand testing skills.
ETL Testing Online Training
Testing Data Integration projects is challenging due to high volumes and heterogeneous nature of data sources. It is a common practice for testing teams to copy records from source and target tables into an excel spreadsheet and manually compare the data for just a handful of records.
What you will learn
However this approach is very limited and prone to errors. Every incremental change to a system increases the scope for functional and performance regression. All these can result in increased cost of ownership, inaccurate insights due to bad data/reports and the loss of trust in enterprise data and reporting capabilities.