You can use tableau data interpreter tool incase you don't want to use concat function.
you can club or combine two columns into one column.
Check this below link it may help you
If you want to combine two strings just add with using + sign
Kindly mark this as helpful or correct if it helps you
Note: JDBC driver if you are using create an extract there are some native tableau functions wont work on live connections
I haven't used Tableau with Spark, but did you try just adding the string? Like [string1]+[string2]?