When you integrate data from multiple data sources, you may run into some of these common issues:
Warning: Cannot Blend Because No Linking Fields
When you drag a field from a secondary data source to the view, you may see a warning that says:
Cannot blend aggregated data from the secondary data source with the data on this sheet because there are no linking fields used in the view.
This warning occurs when you have not used a linking field in the view. For example, if you have two data sources with the related dimensions State and Date, you must be using one of those primary dimensions in the view before you can blend data from the secondary data source.
The secondary data source may not have any relationships to the primary data source. Look in the Data window for the link icon. Tableau automatically links fields that have the same name. If your fields do not have the same name you’ll have to create a custom relationship.
Asterisks Show in the View
When you relate secondary data, make sure that there is only one matching member in the secondary dimension for each mark. If there are multiple matching members you will see an asterisk in the view. For example, say you have two data sources. The primary data source has a state field that contains state abbreviations. The secondary data source also contains a state field along with a customer segment field. Each state may have multiple customer segments (e.g., CA has Consumer and Corporate). When you relate the two data sources on state, you’ve created a relationship where state can have multiple customer segment values. When that happens you will see an asterisk in the view.
All secondary fields are aggregated. Dimensions are aggregated as Attributes (ATTR), which means that if there’s only one member it will show the member value but if there are multiple members it will show an asterisk.
Using a Multidimensional (Cube) Data Source
When blending data in Tableau, multidimensional data sources cannot be used as secondary data sources. These types of databases can only be used as the primary data source.