There should not be any changes in the NSQL Query at all. Here's a really simple example, just so the concept is clear.
* If the NSQL Query is like this:
select
@select:dim:user_def:implied:query0:id:id@,
@select:dim_prop:user_def:implied:query0:full_name:full_name@,
@select:dim_prop:user_def:implied:query0:unique_name:unique_name@
from srm_resources
where @filter@
You will get three fields when you couple this query to a portlet: id, full_name and unique_name.
* Now, just go to Administration -> Studio -> Portlets. Click on New -> Filter Portlet. Fill out the information in the first page. In the second page, click on "Add" and create a "String" field called "full_name".
* Go to the page where you have displayed the portlet created out of the query above, and click on "Personalize". Click on "Page Filters -> Add". Select the "Filter Portlet" created above and Add.
* Here's the most important part. Click on the icon displayed in the second column, of the "Personalize -> Page Filters" page. Once you are in, select "full_name" in the "Mapping Field".
That's it. You have mapped an ordinary portlet's field, to a filter portlet's field. Your filter portlet will now have access to search a column in the ordinary portlet.