I recently noticed that Tableau does not support common table expressions in “Custom SQL” data sources when I was trying to set up a new data source for a dashboard. It is one of those weird gotchas that strikes me as more of a bug than a feature of Tableau. For what I was doing, joining on a transformation of an attribute, it was easy enough to use a subquery within the join clause.
Strangely, CTEs are supported for “Initial SQL” inputs of a data source. ¯\_(ツ)_/¯
Here are some related links: - CTE Table Is Not Working In Tableau ODBC But Working Fine In Hadoop Environment - Using Common Table Expressions
In my opinion, common table expressions and any other features found in the top few SQL dialects should be supported. Otherwise the behaviour is somewhat astonishing.