Calculated column based on different table using Contains (or anything similar)

Hi

I am having problems creating a calculated column based on a column in a different table using the 'contains' function. I either get an error or '[List]'. I want to create a field in tablea that is based on values from fields in tablea and tableb. tablea and tableb are joined on a many to one relationship.

tablea *:1 tableb 

I want something along the lines of:

if contains(tableb[field1], "x") then "new"

else tablea[field1]

endif

With the result to look like the image below:

Any help will be greatly appreciated

Thanks!