What is data blending in tableau?

Data blending in Tableau is used when there is associated data in multiple data sources, which you want to analyze together in a single window. To exemplify, consider the Sales data in a relational database and Sales Target data in a spreadsheet, to compare, you can blend the data based on shared dimensions to get access to the Sales Target measure. The two sources involved in data blending are mentioned as primary and secondary data sources. A left join is formed between the primary data source and the secondary data source with all the data rows from primary and agreeing data rows from a secondary data source.