[Stitch_MS]

А не лучше ли создать новый display метод на таблице с детализацией?

display Comment comment()
{
    ActionTable actionTable;
    Comment comment;
 
    if (this.Comment != '')
    {
        comment = this.Comment;
    }
    else
    {
        select firstonly Comment from actionTable
            where this.ActionId == actionTable.ActionId;
 
        comment = actiontable.Comment;
    }
 
    return comment;
}