Error "Cannot blend secondary data source ... unsupported aggregation"
Published: 20 Sep 2013 Last Modified Date: 06 Mar 2017
When you try to use Count Distinct on a measure from a secondary data source, the following error might occur:
Cannot blend secondary data source because one or more fields use an unsupported aggregation
Tableau Desktop 8.0 and later versions
Consider creating an extract, if a non-additive aggregate is needed on the primary data source, but the data source does not support temporary tables.
Change the dimension to an attribute, if a secondary dimension is being used.
Depending on the data, use the Number of Records field instead of COUNTD.
This error message can also appear when a level of detail expression is used in a view that uses data blending. The linking field in the primary data source must be in the blended view before the LOD expression can be used from the secondary data source.
Note: The above suggestions may not work if linking fields were explicitly added by clicking the link icon in the secondary dimensions window.
Data blending has some limitations regarding non-additive aggregates such as COUNTD, MEDIAN, and RAWSQLAGG. These limitations cause certain fields in the view to become invalid in certain circumstances.