title: Cast to datetime returns null only for columns in MySQL
body: <p>I'm trying to cast a varchar column in MySQL with str_to_date(), the thing is that it works perfectly if you copy the string from the column, like '04/24/2015 00:00:00', but when you try it with the column itself it returns null.</p>
  
  <p>This is my trial query:</p>
  
  <pre><code>SELECT STR_TO_DATE('04/24/2015 00:00:00', '%m/%d/%Y %T'),
  STR_TO_DATE(StartDate,'%m/%d/%Y %T'), StartDate
  FROM TMP;
  </code></pre>
  
  <p>This returns:</p>
  
  <pre><code>2015-04-24 00:00:00  (NULL)  04/24/2015 00:00:00
  </code></pre>
  
  <p>I tried a ton of things but nothing seems to work...</p>
  
  <p>This is the result with HEX(startdate):</p>
  
  <pre><code>2015-04-24 00:00:00 (NULL) 00300034002F00320034002F0032003000310035002000300030003A00300030003A00300030
  </code></pre>
  
  <p>Thanks in advance!</p>