There are two layers in Tableau: Logical and Physical.

The logical layer operates differently of the physical layer. But what are these differences?

Logical Layer and Relationships:
Logical layer is where you create a relationship between tables. when the relationship is created Tableau keeps tables separated and it does not become one single table. The relationship in Tableau looks for fields that match to build a query to bring data from those tables.
One limitation of the relationship is that does not allow to make decision on the join type. However, the relationship affords advantage as select joins based on time and context of analysis.

Relationship Between two tables in Tableau Logical layer:

Relationship Between multiple tables in Tableau Logical layer:

Physical Layer and Joins:

Physical Layer is where the joins can be created between the tables as required. When the join is created Tableau merges the tables and it creates a single table.

To create a join is necessary doble click on the table in the logical layer to open the physical layer and then just drag another table next to it. In the physical layer it possible to choose the type of join and it is more suitable for analysis and visualisation, but it is also a more static way to combine data.

One limitation of the join is the fact that the joins need to be done before the analysis and it cannot be changed without impacting all sheets using that data source. However, the join affords make unions between tables and it also allows control on the way to combine table.

 

Join Between two tables in Tableau Logical layer:

Union Between two tables in Tableau Logical layer:

This information is a summary of Tableau.com page How Relationships Differ from Joins.

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