What kind of JOIN should I use to join these tables?
<p>I have the following three tables that I am trying to join together and create an overview of all desktops and whoever has one assigned to their UserID if any.</p>

<pre><code>dbo.Users
ID    Name     Lastname   JobTitle
118   Ryan     Doe        Field Engineer
119   Jessica  Braun      Technical Consultant
120   Daniel   Sous       Web developer
121   Amy      Amyson     Intern
.. etc

dbo.LightDesktops
ID    Model     MACAddress          UserID
1     HP1234    AA:AA:AA:AA:AA:AA   118
2     HP1234    BB:BB:BB:BB:BB:BB   121
3     HP1234    AA:BB:BB:AA:BB:AA   NULL
4     HP1234    BB:AA:BB:AA:AA:BB   124

dbo.MediumDesktops
ID   Model      MACAddress          UserID
1    HP12PRO    AA:AB:AA:BB:AA:BA   132
2    HP12PRO    BB:BA:AB:BA:BB:AA   119
3    HP12PRO    AA:BA:BA:AB:AA:BA   123
4    HP12PRO    BB:BB:BB:AB:BA:BB   241
</code></pre>

<p>I managed to figure out how to do it per type of desktop, for example LightDesktops:</p>

<pre><code>SELECT * FROM LightDesktops LEFT OUTER JOIN Users ON LightDesktops.UserID = Users.UserID
</code></pre>

<p>That will show me a nice overview of the light desktops with their information as well as whoever has one assigned to if any.</p>

<p>If I'd like to have an overview of the light desktops that are not used and therefore in stock I can do</p>

<pre><code>SELECT * FROM LightDesktops LEFT OUTER JOIN Users ON LightDesktops.UserID = Users.UserID WHERE LightDesktops.UserID IS NULL
</code></pre>

<p>How can I accomplish the same results, but for both tables containing information of our desktops? I tried to use an UNION but returned me lots of duplicate values.</p>