how to do joins on prompt queries in report studio?

[ejaycognos]

I have a report where there are multiple prompt queries got from single table , the final prompt I need to get from different table ie from union query(its a union of 3 tables).

prompt 1 ------

prompt 2 ------

prompt 3 ------ All these 5 prompt are got from TABLE 1

prompt 4 ------

prompt 5 -------


prompt 6 ------- Need to get from Union Query (which in turn combination of 3 queries)

In the prompt page , under value prompt properties , under Data Query if I try to just pull the Query from "union query" and click on use and display the required value,

I am getting cross joins eroor between these query subjects xyz is not allowed for {All Authours ,etc..}

I know I need to do joins between these query subjects but what join and cardinality to use ?
I need to like one field "Employee Name"


Thanks