title: sql query for posts with specific tags
body: <p>I have posts, tags, post_tags tables.</p>
  
  <p>Now I want to get all posts that have (a, b, d) tags, </p>
  
  <p>how do I achive that and not only getting all posts with one/two/all tags?</p>
  
  <pre><code>tables:
  
  posts:
  id, title
  
  tags:
  id, title
  
  post_tags:
  post_id, tag_id
  </code></pre>
  
  <p>my simple idea was this query:</p>
  
  <pre><code>select *
  from post_tags pt
  join posts ps on pt.post_id=ps.id
  where pt.tag_id in (MY_DESIRED_TAGS)
  </code></pre>
  
  <p>this surely doesn't work as i get posts with only one of the tags and not all of them.</p>