title: MySQL select 3 first characters and replace
body: <p>I have a simple problem, which is causing me problems</p>
  
  <p>I have a column in mysql with names, and I'd like to replace these by the first three characters in the name. 
  So for instance 'Jacob' -> 'Jac'. </p>
  
  <p>I know of the LEFT command, which can do this for me, but I can't seem to update the column with the output. Like I can do a select, and then get the correct output, but I can't update the desired column with the output :(</p>
  
  <p>I tried:</p>
  
  <pre><code>REPLACE INTO mytable(shortnames) SELECT LEFT(names,3) FROM mytable;
  </code></pre>