title: Forum MySQL query
body: <p>I need help with a sql query</p>
  
  <p>I have this table (post_table):</p>
  
  <pre><code>+----+---------+--------+
  | id | topicId | userId |
  +----+---------+--------+
  | 1  | 1       | kalle  |
  | 2  | 1       | pelle  |
  | 3  | 2       | laban  |
  | 4  | 2       | kalle  |
  | 5  | 2       | kalle  |
  | 6  | 2       | kalle  |
  | 7  | 1       | kalle  |
  | 8  | 1       | kalle  |
  | 9  | 2       | laban  |
  | 10 | 1       | laban  |
  | 11 | 2       | kalle  |
  | 12 | 2       | kalle  |
  | 13 | 3       | laban  |
  | 14 | 1       | kalle  |
  | 15 | 2       | kalle  |
  | 16 | 1       | kalle  |
  | 17 | 3       | laban  |
  | 18 | 4       | laban  |
  | 19 | 5       | laban  |
  | 20 | 6       | pelle  |
  +----+---------+--------+
  </code></pre>
  
  <p>I want to get only the rows where userId "kalle" have not read the post, they are</p>
  
  <pre><code>+----+---------+--------+
  | id | topicId | userId |
  +----+---------+--------+
  | 13 | 3       | laban  |
  | 17 | 3       | laban  |
  | 18 | 4       | laban  |
  | 19 | 5       | laban  |
  | 20 | 6       | pelle  |
  +----+---------+--------+
  </code></pre>
  
  <p>topicId 1 was already read by userId "kalle" in id 1,7,8,14</p>
  
  <p>topicId 2 was already read by userId "kalle" in id 4,5,6,11,12,15</p>
  
  <p>And then I also would like to get the unique values in topicId, either id 13 or 17 can show up but not both.</p>
  
  <p>I hope you understand what I'm after</p>