title: Selectively applying user ID in WHERE clause to entries
body: <p>I been going back and forth with IF and CASE and a whole lot of other suggestions found elsewhere trying to figure out how to filter out certain entries based on category and user ID. Assume that a table <code>user_posts</code> contains posts made by a lot of users. I want to get results restricted to the <code>user_ID</code>='MIRA76' for posts that are in categories 'CAT_64' or 'CAT_106'. However, I still want to get results by other users from other categories.</p>
  
  <p>TABLE <code>user_posts</code></p>
  
  <pre><code>+----------+--------------+----------+-----------------+
  | post_ID  | category_ID  | user_ID  |     content     |
  +----------+--------------+----------+-----------------+
  | 456FQ    | CAT_64       | MEK90    | TEXTUAL CONTENT |
  | 754GD    | CAT_21       | MEK90    | TEXTUAL CONTENT |
  | 616CZ    | CAT_106      | MIRA76   | TEXTUAL CONTENT |
  | 714PA    | CAT_64       | MIRA76   | TEXTUAL CONTENT |
  | 554WU    | CAT_26       | RON32    | TEXTUAL CONTENT |
  | 451YD    | CAT_41       | RON32    | TEXTUAL CONTENT |
  | 783TD    | CAT_21       | MIRA76   | TEXTUAL CONTENT |
  | 156GL    | CAT_11       | MEK90    | TEXTUAL CONTENT |
  | 274HD    | CAT_11       | HOM92    | TEXTUAL CONTENT |
  +----------+--------------+----------+-----------------+
  </code></pre>
  
  <p>In the example entries, for categories 'CAT_64' and 'CAT_106' only those by the <code>user_ID</code> 'MIRA76' is taken, but for other categories there is no such restriction. How do I go about doing this? Here those other than the first one are the ideal results.</p>