title: Mysql only update if where data is in latin8
body: <p>I have this statement which works in the first run</p>
  
  <pre><code>UPDATE accounts SET username = CONVERT(CAST(CONVERT(username USING latin1) AS BINARY) USING utf8)
  </code></pre>
  
  <p>This would convert latin1 characters into UTF8 chinese character in mysql.</p>
  
  <p>Running it the <strong>2nd time</strong>, the character will become weird.</p>
  
  <p>How do I add in a <strong>where condition</strong> that only update username to utf8 from latin1 if the word is currently in latin1 </p>