The video tutorial explains how to merge data from different sources using Power BI. It begins with an overview of various data sources like Excel, CSV, SQL, and Hadoop. The tutorial then demonstrates how to prepare and load data files into Power BI, specifically focusing on a master Excel file and a transactional CSV file. Finally, it details the steps to merge these files using Power BI's query editor, highlighting the use of a left outer join to bring a salary column from the master table into the transactional table.

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