title: SQL Get unique value of group id where member id is one or more
body: <p>I need some help with some code</p>
  
  <p>I have a database table called "stuff" and I have this info:</p>
  
  <pre><code>+------+-------------+---------------------+
  | id   | member_id   |     group_id        |
  +------+-------------+---------------------+
  | 1    |      11     |         aa          |
  +------+-------------+---------------------+
  | 2    |      11     |         bb          |
  +------+-------------+---------------------+
  | 3    |      22     |         bb          |
  +------+-------------+---------------------+
  | 4    |      11     |         cc          |
  +------+-------------+---------------------+
  | 5    |      22     |         cc          |
  +------+-------------+---------------------+
  | 6    |      33     |         cc          |
  +------+-------------+---------------------+
  </code></pre>
  
  <p>what I need:</p>
  
  <pre><code>If I search for group_id when member_id = 11 the result will be aa
  If I search for group_id when member_id = 11 AND member_id = 22 the result will be bb
  If I search for group_id when member_id = 11 AND member_id = 22 AND member_id = 33 the result will be cc
  </code></pre>