Select two first characters and ignore duplicates
<p>I'm currently working on a MySQL database that stores lots of unique postcodes. This is how it looks like:</p>

<pre><code>postcode_id | postcode
     ------ | ------
        1   | BA10EJ  
        2   | TR96PY 
        3   | TA64RD 
        4   | EX54NA 
        5   | EX167DT
</code></pre>

<p>I'd like to select the first couple characters and only list the unique ones, so if there are two EXs I just need to display EX once.</p>

<p>This is what I'm trying to get:</p>

<pre><code>postcode
 ------
   BA  
   TR 
   TA 
   EX
</code></pre>