title: MySql - IN operator (with exact values)
body: <p>Table "argument_user"</p>
  
  <pre><code>+-------------+----------+
  | argument    | user_id  |
  +-------------+----------+
  | bike        | 1        |
  | flower      | 2        |
  | web         | 1        |
  | web         | 2        |
  | nature      | 1        |
  | nature      | 2        |
  | nature      | 3        |
  +-------------+----------+
  </code></pre>
  
  <p>I want get ONLY the arguments in common with user 1 and 2 >> "web" (without "nature")</p>
  
  <pre><code>+-------------+
  | web         |
  +-------------+
  </code></pre>
  
  <p>Now I'm using this query, but it's wrong because it returns me "web" and also "house". </p>
  
  <pre><code>select argument from argument_user 
  where user_id in ('1','2') 
  group by argument having count(distinct(user_id)) = 2
  
  +-------------+
  | web         |
  | nature      |
  +-------------+
  </code></pre>
  
  <p>I thought to do a join with the same table, but i think it's too heavy when the users will be more! don't you?
  So, something light to use with a lot of "user_id".</p>