Tableau 2020.2 brings a much simpler and powerful way to combine data – using relationships. Relationships describe how two or more table relate based on a common field but does not merge the two table together like in the case of joins. Therefore, when relationships are created between tables, each table remain separate hence retaining their individual level of details. Then Tableau brings data from these tables to create a viz – with Tableau figuring out the right join type and how to deal with nulls.
In order support both relationships and traditional ways on combining data (joins and unions), the Tableau 2020.2 data model in the data source contains a logical layer (default way of combining data) and physical layer.
Logical layer – Where you can add multiple tables and relate them based on a common field
Physical layer – where you can combine data through joins and unions
(Double click on a logical table to open the physical table where you can do joins and unions)
Relating tables based on a common field
Joining tables on the physical layer
(Double click on a logical table to access the physical table)
Take a way on relationships
Relations require you to select the matching fields only, no selection of join types
Tables maintain their level of details in the data source and during analysis
No duplicated aggregated values
During analysis relationships automatically create appropriate joins based on the fields in the view
Tables are not merged in the data source
Relationships make all rows and columns from the related tables potentially available in the data source
