title: Combining 3 separate columns into one for it to be used in an IN clause
body: <p>This is purely an efficiency question. I have two tables:</p>
  
  <p>One where user IDs are stored based on their position within an entity</p>
  
  <pre><code>id     | supervisor     | manager      | worker
  -------+----------------+--------------+---------------
  1      | 12             | 15           | 32
  2      | 12             | 42           | 22
  </code></pre>
  
  <p>And the one with the user info:</p>
  
  <pre><code>id     | name           | email
  -------+----------------+---------------------
  12     | Bob            | bob@example.com
  15     | Dave           | dave@example.com
  </code></pre>
  
  <p>Is it possible to do this with only one <code>IN</code> clause instead of 3?</p>
  
  <pre><code>SELECT `name`, `email` 
  FROM `tbl_users` 
  WHERE `id` IN 
  (SELECT `supervisor` FROM `tbl_warehouse` WHERE `id` = 'WAREHOUSEID') 
  OR `id` IN 
  (SELECT `manager` FROM `tbl_warehouse` WHERE `id` = 'WAREHOUSEID')
  OR `id` IN 
  (SELECT `worker` FROM `tbl_warehouse` WHERE `id` = 'WAREHOUSEID')
  </code></pre>
  
  <p>I tried a few things trying to combine the <code>supervisor</code>, <code>manager</code>, <code>worker</code> columns into one column so the <code>IN</code> clause works but did so without success</p>