title: Django DateTimeField date filter not working
body: <p>I have a <code>DateTimeField</code> named <code>created_at</code> in my model. I Would like to query the objects which are created today. From <a href="https://stackoverflow.com/questions/1317714/how-can-i-filter-a-date-of-a-datetimefield-in-django">this question</a> I have used the following query set,</p>
  
  <pre><code>In [70]: today = datetime.datetime.today().date()
  In [72]: Business.objects.filter(created_at__date=today)
  Out[72]: &lt;QuerySet []&gt;
  </code></pre>
  
  <p>It returns zero results. I have make sure that there is an entry in the database, which was created today. I know that I can also use </p>
  
  <pre><code>Business.objects.filter(created_at__contains=today)
  </code></pre>
  
  <p>But it yields results with a warning:</p>
  
  <pre><code>django/db/backends/mysql/base.py:71: Warning: (1292, "Incorrect datetime value: '%2017-12-21%' for column 'created_at' at row 1")
  </code></pre>
  
  <p>I'm using MySQL database. My Model is</p>
  
  <pre><code>class Business(models.Model):
      name = models.CharField(max_length=255, blank=True, null=True)
      url = models.CharField(max_length=255, blank=True, null=True)
      created_at = models.DateTimeField()
      category = models.CharField(max_length=120)
  
      class Meta:
          managed = False
          db_table = 'Business'
          unique_together = (('name', 'url'),)
  </code></pre>