The data blending brings data from two different data sources together in a single view or in a single Tableau worksheet.
For data blending in Tableau, there are two data sources; a primary data source and a secondary data source.
The relevant data of the secondary data source is taken and added with the main data of the primary data source and a blended table is displayed.
Blending is different from creating joins because blending only combines relevant data from different data sources, whereas joins work on a row-level and often duplicates data that is repeating in several rows.
Also, both data blending and joining create a left join between two data tables.
But the main point of difference is when the aggregation takes place, that is, when a join is created, the data is combined first and then aggregated.
Whereas, in data blending, the data from primary and secondary data sources are queried independently, aggregated, combined and then used for visualization.
So, the order of operations are different in both.