title: MySQL : strange LENGTH() behaviour on utf8 string
body: <p>I am doing unit tests on requests generators, and I get in trouble with <code>LENGTH</code> function.</p>
  
  <p>I have 2 requests that follows each other :</p>
  
  <pre><code>SHOW VARIABLES LIKE '%character%'
  </code></pre>
  
  <p>Returns the following result :</p>
  
  <pre><code>array(8) {
    [0] =&gt;
    array(2) {
      'Variable_name' =&gt;
      string(20) "character_set_client"
      'Value' =&gt;
      string(4) "utf8"
    }
    [1] =&gt;
    array(2) {
      'Variable_name' =&gt;
      string(24) "character_set_connection"
      'Value' =&gt;
      string(4) "utf8"
    }
    [2] =&gt;
    array(2) {
      'Variable_name' =&gt;
      string(22) "character_set_database"
      'Value' =&gt;
      string(6) "latin1"
    }
    [3] =&gt;
    array(2) {
      'Variable_name' =&gt;
      string(24) "character_set_filesystem"
      'Value' =&gt;
      string(6) "binary"
    }
    [4] =&gt;
    array(2) {
      'Variable_name' =&gt;
      string(21) "character_set_results"
      'Value' =&gt;
      string(4) "utf8"
    }
    [5] =&gt;
    array(2) {
      'Variable_name' =&gt;
      string(20) "character_set_server"
      'Value' =&gt;
      string(4) "utf8"
    }
    [6] =&gt;
    array(2) {
      'Variable_name' =&gt;
      string(20) "character_set_system"
      'Value' =&gt;
      string(4) "utf8"
    }
    [7] =&gt;
    array(2) {
      'Variable_name' =&gt;
      string(18) "character_sets_dir"
      'Value' =&gt;
      string(26) "/usr/share/mysql/charsets/"
    }
  }
  </code></pre>
  
  <p>My second request is :</p>
  
  <pre><code>SELECT LENGTH('重庆') as len
  </code></pre>
  
  <p>It returns 6 instead of 2.</p>
  
  <p>What's wrong here ? My charset parameters looks good.</p>