This example shows how to display only some columns.
I used the following sql query to get 4 fileds (id,rating,title,votes):
$params['sql_query'] = 'SELECT id,rating,title,votes FROM imdbtop250';
And added column 1 for a list of checkboxes, and column 6 for doing the actions of editing and delete an item.
So now the total is 6 columns (CHECKBOXES + ID + RATING + TITLE + VOTES + ACTIONS)
But now i hide the 2nd column (ID):
$params['display_cols'] = 'tftttt' // t - shows; f - hide;
And still use the ID value (#COL2#) in the checkbox column and in the actions column, despite being hidden.