Tableau 10 Join Calculations

Tableau 10.2 introduces join calculations, allowing string parsing and other operations to be applied to the native database fields to produce matching fields that can be joined. In the following example we want to join a table containing project and sample fields with a table containing those same fields embedded in a workflow name string.

We start by building calculated fields for the secondary data source to parse the project and name from the workflow Name string. Use nested SPLIT commands in this case.

We then can use those debugged calculations directly in the Tableau join window.

Note that this differs from Tableau blending using calculated fields, in that blending only adds columns to a data source, while a join can add rows. In this case we add several rows from WORKFLOW for each project and sample from the PROJECT_SAMPLE_REQUESTS table, each with its own Status. Joins are also much faster than blends.

Although Join Calculations were introduced in Tableau 10.2, they can be converted to Custom SQL and used in older versions of Tableau. In this way Tableau 10.2+ can be used as an SQL code generator.

https://community.tableau.com/thread/247362