title: Check if values are not exists with WHERE IN clause - MYSQL
body: <p>Hey im writting sql query, I almost done it but I need to change important thing but still dont have idea to repair it. There is my SQL example</p>
  
  <pre class="lang-sql prettyprint-override"><code>SELECT post.id,post.name as post_name,
  (SELECT users.login FROM users WHERE post.creator = users.id) creator,
  (SELECT COUNT(*) FROM recommends WHERE recommends.idea_id = post.id) recommends,
  (SELECT COUNT(*) FROM comments WHERE comments.idea_id = post.id) comments,
  GROUP_CONCAT(tags.tag SEPARATOR ',') as tags
  FROM posts
  LEFT JOIN tags
  ON post.id = tags.idea_id
  WHERE post.name IN
  (
      SELECT post.name FROM posts
      JOIN tags   ON post.id = post.idea_id
      WHERE tags.tag IN ('X','Y','Z')
  )
  GROUP BY post.name
  </code></pre>
  
  <p>What's the problem? If our X or Y or Z is not exist the query still working. I dont know how to repair, i tryed some NOT EXISTS clauses or NOT IT but it not working. 
  Thanks for help.</p>