Joins: Data Blending
Data blending is one of Tableau's more powerful features, it allows data from multiple sources to be brought together and used in the same view, in an interactive way. Like joining, blending uses a key field present in both datasets to establish a relationship between them, the primary and the secondary.
The Primary Data Source
To blend data the first thing you need is two datasets, the first your primary dataset, this will often be the larger of the two. The other will often be smaller and will be supplemental data you want to blend into the primary data source. Connect to the two data sources as normal.
Connecting to The secondary Data Source
The Secondary Data
Before you start building your view you need to check that the relationships between the two datasets are well defined, to do this go to the data menu and select edit relationships here you can see how you define relationships between the primary and the secondary datasets and deciding which fields you wish to use to blend the two datasets on.
Editing the relationship between the two datasets
Tableau will look at the two datasets and try to find a common dimension name to blend on, this can be customised if the chosen field is not the one you wish to blend on.
The Edit Relationship dialogue
Once the relationship is defined you can start building a view using your primary data source to begin with (The data source of the first element added to a view will determine which data source tableau sees as the primary data source).
Building the map using the location field
Once you have the elements in place from your primary data source begin drawing in additional elements from your secondary data source
Adding the Salary to the view.
If you ever happen to forget which is the primary and which is the secondary tableau uses a simple visual clue to help you identify them:
Primary vs. Seccondary
The Datasource with the blue checkmark is the primary data source and the one with the orange check is the secondary source.
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