The CAST expression is a fundamental part of the SQL standard and you cannot suppress it entirely from the queries Tableau generates. This sounds like it may be a problem with the ParStream SQL parser, and I encourage you to report it to their technical support team.
On a related note, I have seen a few other issues reported that involved seemingly unnecessary casts of a string type to a VARCHAR(100), and I believe that this problem is currently being investigated. Once addressed you may no longer see this particular query expression, however you may continue having problems with ParStream if it is unable to handle the CAST syntax Tableau may use in other circumstances.
We are using Generic ODBC driver with Denodo and Snowflake as the backend. The query always does a CAST(String column VARCHAR(100)), this works fine in Redshift but throws an error in Snowflake since the values in the column are more than 100 characters and the CAST does not work.
What are our options? Snowflake says this is not an ANSI SQL implementation.
Appreciate your help.