title: split string by chunk length in mysql
body: <p>I have a string like this: <code>0002000B0016001M001S002A</code>
  (variable string length but divisible by 4)</p>
  
  <p>I need to split it (in MySql) in chunks of 4 characters</p>
  
  <p>Espected result :</p>
  
  <pre><code>@my_var = '0002'
  
  @my_var = '000B'
  
  @my_var = '0016'
  
  @my_var = '001M'
  
  @my_var = '001S'
  
  @my_var = '002A'
  </code></pre>
  
  <p>I think SUBSTR() can be employed here but I don't know how to manage next position in a loop in mysql</p>
  
  <p>Or some equivalent like chunk_split() in PHP for MySql?</p>