How to show only one duplicate?

This is kind of an extension of this question of mysql not in or value=0?

I have two databases one has the widget information and the other is the layout of those widgets according to the module. On the page I have lists to put these widget such as Header, Content, Sidebar, and Footer. There is also a list of widget that are not being used. That is where I am having the problem.

Here is the mysql that I am using:

SELECT *
FROM widgets AS w
    LEFT JOIN widget_layouts AS wl
        ON w.id = wl.widget_id
WHERE wl.widget_id IS NULL
    OR wl.module_id <> '2'

This displays all of the widget that don't have module_id of 2. So if I put one of the widge开发者_JAVA技巧ts into another list it will still show up in the unused widget list because it is also being used by another widget.

Here is the table of widget_layouts:

|Module_id | Widget_id | Position | Weight|
-------------------------------------------
|2         |3          |1         |0      |
|1         |9          |3         |3      |
|1         |8          |3         |2      |
|1         |3          |2         |1      |

So here is the question:

How do I display a list of widgets that are not being used by module 2 or don't exist?

EDIT:

I am going to try to clear up of what I am trying to do. I want a list to show the widgets that are not in the list and widgets not being used by module 2 but if it is being used by module 2 then don't display that widget.

I have two lists one for content and one that displays available widgets. So when I drag widget 3 from the widget list into the content list. Then to a browser refresh there are two widget 3 that are displayed, one in the content list and one in the available list.

So how do I show widgets that are not in the database and if the widget is used by module 2 it does not show up in the available list?

---

You can group columns with the same values with SQL:

SELECT widget_id
FROM widgets AS w
    LEFT JOIN widget_layouts AS wl
        ON w.id = wl.widget_id
WHERE wl.widget_id IS NULL
    OR wl.module_id <> '2'
    GROUP BY widget_id